Well, the argument would be that in-game, RH enemies never move intelligently to avoid traps, they just move either randomly or else predictably INTO traps of their own volition. What Elf mentioned about traps having a weakness is fair, but that weakness in-game is almost exclusively unpushable enemies / enemies that take the entire grid, something that doesn't come up so often outside of Godlike in the DL. I can see a holistic argument that "traps aren't hosed as often in the DL as they are in-game, nerf them," but what Pyro was referring to is surely that in-game, Aht will have support with stuff other than Push Assault to ensure the trap connects, something she doesn't have in the DL, so it balances to a degree.
My own personal complaint with allowing this cart-blanche to any opponent is that allowing RH grid movement should, to me at least, absolutely allow the damage reduction / increasing effects as well, or else we're really hacking the system to pieces. So characters like Rosch get randomly hosed by Boco or whatever who goes and cowers in the back while spamming Choco Cure and countering, which is kind of weird. Anyway, as for me, I think that characters with a cleanly legal move command or row switch command can go play the 50/50 guessing game with Aht if they want, just that doesn't include Lexis. But this actually does include a reasonably large swathe of the DL, like most FF characters or strat-RPG characters, so seems fair enough at reflecting in-game.
Incidentally, did RH enemies with guns / other ranged weapons in the back row do reduced damage? If so, then Aht might beat Lexis anyway given either status protection or no starting IP hype, because Lexis would fail to 2HKO Aht despite the switch bonus, and Aht's Cross Star damage doesn't care about row IIRC, so she'd just heal until a double -> Switch -> 3HKO.