Theirs is less defense and more cheap tactics. Those tactics are not viable at a higher level simply because they are so damn punishable. Lots of vulnerable frames where they're doing nothing. If Yu is spamming his DP repeatedly, just fake advances, like run it him then immediately start blocking, likely they'll just DP into your block and then you fuck them up. Do it a few times, then if they start to stop doing it, suddenly attack at seemingly random times, it becomes incredibly difficult for them to figure out whether or not you'll just block their DP or not.

For Adachi if they spam the 2D, or 5D, the solution is easy. 5D, blocking it will give you around 15-20 meter, and you'll far outstrip Adachi in meter. 2C is simple, just watch for the animation. The move is blockable under all normal circumstances, so it doesn't hit overhead or low, making it easy to block. Once you block it, just instantly 5A and take his Persona from him. Once he has no Persona, the kick is a problem? Nah. It's worse than Sho's kick, but still good and requires more timing. The way you deal with that depends on characters, but it's not difficult to deal with especially if Adachi isn't mixing his game up.