The problem is, Izuna is very unreliable. I mean, I can do it, but only like 50% of the time I try. And going for their backs is what I usually do, in fact… However, FA -> backdash is a really safe option: if your walldive hits from the front, they absorbed the damage and got into a safe position, and if if you hit fron the back… you eat the aforementioned big combo. FA->backdash shuts down the walldive, unless your control of it makes you land Izuna like 80-90% of the time. I just can’t do that, considering how they implemented it in this game.
As for the moves that simply beat the walldives, well, air to air there’s almost always a combination of timing and steering that beats those. The good ones on the ground, yes, those are really hard to avoid.