It IS a problem specific to SD.
Sure the same busted units that everyone plays and complains about are present in other game modes, but here is the thing: the AI is incredibly dumb and will give you opportunities to exploit (except maybe for F!Edelgard. She does have counters, but she doesn’t have a real vulnerable moment once transformed, unlike Yuri or BEirika).
However, in the player’s hands, those opportunities become much rarer.
The only solution is to create the opportunity, but with the many tools meta units have to prevent you from doing so without endangering your whole team, unless you play those units yourself, you’re gonna have a bad time.
(As a side note, the very concept of PvP in FE effectively makes any EP strategy irrelevant, which is a problem in and of itself)
Tbh, that was a rather predictable outcome. The game has never been balanced around true PvP. AR was already, in some ways, proof of that, despite lacking any direct intervention from the defense player. IS’ history with PvP should have been a sufficient warning for those who asked for it. They never managed to make a decent one.