The biggest frustration of FIFA 20 was defending. AI or Human Opponent running around my player but my AI controlled teammate won't react. He will not bother to stick out his foot or any sort of pressure. Only the player selected will respond. Even then they are so static, sometimes so naive that opponent would run straight pass him only to score near post.
The solution? Constant Pressure and Possession play.
Forget stamina loss, as they say. It does not loss that much. Any by the 70th minute when stamina do deteriorate for few, you are already up by 1 or 2 goals if not more. And you can substitute 3, so who cares?
Just make sure your defensive width is 7/8, and depth is minimum 5. Wide width is important imo, as narrowing means wide players have to run from narrow areas to wide to close down wide attackers. Do track back manually with your double pivots in 4231. Stick with the opponent, come close, they will do the stand tackle for you. Also the AI controlled teammate will be super responsive, especially closing down the ball carrier and sticking legs at will.
Still you have to be a little patient while defending, and smart to not move players out of their position too much, especially the defenders. But without CP tactics this patience does not pay off.
Yes, you will face some highly skilled players in Seasons of FUTs, that might edge past you, but who wins all the matches anyway? The average or good players who defend deep or balanced or whatever will not frustrate you anymore.
Another vital thing is while attacking, play patient, or possession game. The more you keep the ball in your feet less stamina loss. As you do CP, it is for them to panick when in possesion, not you. Atleast that is how I ended my frustration of lossing for my silly AI teammates.