Good questions:
First, the 3-4 isn't represented well in Madden because Madden doesn't represent gap control/assignments. Technique doesn't matter, only ratings and a dice roll. Size and strength don't matter on the field either. In the 3-4, the defensive linemen are asked to play 2 gaps. They aren't asked to play any gaps in Madden. There are no concepts of having a force man, or getting hooked, or anything like that which go into the real life trench battles against a 3-4 or 4-3 front.
Second, Madden doesn't represent pass protection properly on the offensive side of the ball, which in turn affects you bltiz schemes. You don't "cause confusion" in blocking schemes. Heck, if you
do get a "free rusher" at the QB, they game will just slide over a back side offensive linemen to pick him up. The game knows who is coming and from where. The game knows your plays. You can't out scheme the computer. You just win or lose dice rolls based in part on ratings, though mostly on the difficulty settings and slider adjustments.
Third, Madden lacks a number of plays in the 3-4 that it has in the 4-3. Just a quick look through the Facebook Madden 25 playbook AP, to get these images, and here are some examples:
There are number of other examples, but I don't like digging through that ap. It is a real pain to find what I am looking for.
Next, "What if the DE you move inside is a speed guy" Um, you shouldn't have "a speed guy" at DE if you are trying to play the 3-4. He should be a big mauler DT type. Otherwise, you are playing 4-3 style, right?
The main thing to me, is as a coach of real football, but a fan of playing football video games, I try to stick to "realistic" strategies and call as much as possible. Madden plays more like High School football at best rather than NFL level football, but it is what it is. I can play a more realistic 4-3 scheme with my 3-4 aesthetics.