dieaready Walls are strong because width is strength, but if depth becomes strength because of boarding mechanics or hangars or speed being valuable walls just get a bit thicker, they don't stop being walls.
Against a multivector attack the strongest move is always to back out. Because of the way engines are mounted a wall or in the extreme case a single facing square can always be made as fast as a slimmer ship. If defenses are needed along the flanks while withdrawing, the wider a wall is the less it has to spend on them in proportion to its total size.
Even if you have multiple facings the strongest move is still to back out so you can rotate in fresh facings instead of having them all attacked, and a single facing wall has more space for engines to back out.