Three things that are really frustrating me... and I really hope you'll fix them in Pro Football 2021....
1) Coverage.
a) When creating a play, when using a pre-made play... there is no way to pick who covers whom in man coverage. It's hard to create gameplans built to focus on taking one player out of the game (double or triple covering a specific player for example), because all you do is set 'cover man'. It doesn't specify which player to cover. I built a play on offense where my tight end basically runs down the middle of the field. I've seen several plays where the coverage all move away from the middle of the field leaving him WIDE OPEN. That should never happen. Same with FB, which is why I like a fast FB who I can send out on a pass route. He is OFTEN not covered. I have tested a full gameplan where my FB is my main weapon. He gets 130-150 targets a season, almost always getting over 1000 yards receiving, because he isn't covered often.
b) It doesn't specify what kind of coverage to use (bump and run, man, back off, inside, outside...). You have no real control over actual coverage assignments. If a team is constantly using an out pattern with a lot of success, I would LIKE my CB to play outside coverage... in other words, line up outside of the receiver, where he can be in a position to make a play. Also, if I have slow CBs or the opponent has very fast WRs, I'd like to play off them, giving up short plays but not getting beat deep. This is especially important on blitzing plays, where there is single coverage. And if I have strong CBs against weaker WRs, I'd love to get up there and play some bump and run, giving my pass rushers time to get in on the QB.
There are literally NO options available for playing pass defense.
Fix for this...
a) Give every possible receiver a # in each formation... WR1 is #1, WR2 is #2, TE is #3, RB is #4, FB is #5 in base formation, WR3 is 3, TE is 4, and RB is 5 in Spread, etc. Then, when building a defensive play, when you choose man coverage, you also can choose which player to cover (1-5). So I could double the TE if I wanted, or even triple cover. In the play options, allow a choice of whether to be in base formation or line up over coverage responsibility... So, if I'm in nickel against Spread, and I want my nickel CB to blitz, and I want my SS to cover the slot receiver... I choose yes (or no, whatever) to have the SS line up over the slot receiver he will be covering.
b) Add options to man coverage how to line up. Bump and run plays right up on the receiver, man would give the normal cushion, off would give an extra 5 yard cushion, etc.
How this adds value... Right now, you are building a defense based on your player's abilities. You have no strategy adjustments to make to defend against a team's best players or plays. With the custom play creator, you'll start finding there are plays which will be unbeatable... because you can do a lot on offense, but the defense cannot counter. This is a way to help defend the undefendable plays, keeping the game balanced and still allowing myriad strategic possibilities.
2) Play calling, specifically blitzing.
This is my biggest single pet peeve. We have ZERO control over blitzing. I can say I want to blitz 20% of the time, but I cannot even pick which blitzes I want the game to use. Blitzing is basically a game of chance, rather than a viable tactic. When I choose 20% blitz, and a blitz is called, I'm rolling the dice on a useful play. I can't say don't use this blitz, or use this blitz, etc. We can't even SEE the blitzes available to us and that the game will use. There is a workaround which is creating your own blitzes and putting them in your playbook, but not everyone is a fan of creating plays... so it's only reasonable to give players control over what blitzes to use. At worst, players should be allowed to see the blitzes and choose which ones to use or not use. At best, you can be given the option to remove blitz calling, and just create a playbook with the blitzes you want as part of it, with appropriate frequencies just like any other playbook. So, instead of the AI choosing which blitz you run, YOU can choose it. Blitzing is a VERY important strategical part of defensive gameplanning, and more control over it shouldn't be an option, it should just be. When you blitz, you are rolling the dice... but you are at least in control of how you will go about rolling the dice. The way the defensive gameplanning is now, you just plain roll the dice, and if you choose not to blitz, you are wasting a very valuable addition to your defensive gameplan. For the most part, I don't blitz more than 25% of the time (except 3rd and long, hahaha), but when I blitz, I'm blitzing with specific intent. A small example is I'm playing a guy that like to run off tackle to the strong side often, and does very well doing it... well then I'll just throw down a blitz into that area with my SS or LOLB or both... and help disrupt and shut down that run. Better, if it's a pass, I've just added a little extra pressure. Fact is, you don't want to gamble all the time like this, but throwing it in there really helps either exploit a weakness or disable a strength, and that's basically what defensive gameplanning is all about.
3) Aiming your pass rush (and blitz). Right now, pass rushers rush straight up, blitzers blitz straight up... it's really easy to create an offensive gameplan to foil the defense you are up against, because there is no variety. You know what you'll get. Offensive linemen can block their area, or move to help other areas, but your defensive linemen only run straight. Again, if a team likes to run left most of the time, then you can have your linemen all rush to their right (the offense's left) to help get a push in that direction. Again, just like on offense, where your offensive linemen can run block left, right and center, your defensive linemen should have the same option.
To fix this is simple, Instead of rush, put rush left, rush center, rush right. Blitz right, blitz center, blitz left. You can already do that with pass blockers, so it should be easy to put in for rushers.
Now here's the hard part... stunts. Using stunts a lot is like blitzing... it's bad. You often leave a gaping hole somewhere in your defensive line when you stunt... much like a pulling linemen on offense. But there are times and places where a stunt is necessary. For example, let's say I don't want to blitz, but my opponent has a tendency to run that off tackle to the strong side in base formation. Well, instead of blitzing, I can have my right DT stunt left, basically moving a third linemen to the point of attack. If it's a counter, I'm screwed, as there's a huge hole there. Another dice roll, but one I'm willing to take occasionally. Also great for pass rushing on passing situations, but again make you susceptible to draws or QB scrambles... If you're playing a nice zone defense on 3rd and 12, you can feel comfortable in running a stunt, leaving 7 guys in coverage, and not giving up a big play on a draw or QB scramble... but zones are also easily beaten with the right play calls.
Overall, there's a LOT of interesting strategic possibilities on defense. And as I gameplan, it becomes increasingly frustrating to me. The main reason is simply you have so much great stuff in this game, giving so many opportunities for regular Joes like us to have a chance to experience the strategic situations that NFL or other coaches need to go through to be successful. There's a lot of great stuff, but so much of it is unusable or not used in a useful way. In all, offense has a lot of flexibility and opportunity to do creative things... defense does not currently. I really hope that, in future versions, you level this out so defense has the same variety and opportunity that offense has.
Finally, if you do some or all of this, and you need some help in creating the base plays and playbooks for defense, I will be ECSTATIC to be able to help you create these. This is what I enjoy the most about this game, and it would be literally fun for me to help.