Legion is just as much a train wreck in some ways. In WOD we joked about spamming Whirlwind because in mid beta you could do that and be pretty close to optimal, but that changed and so the "spam whirlwind" never made it to live, even though people still used the joke.
Legion Arms really is no joke though, you really do spam slam and guess what happens when you move to 2 targets? You spam Whirlwind is what happens. Now also subject to tuning is the fact that we have Cleave ability which is useless on Cleave and only worth using at 4+ targets, where we Cleave and then Spam whirlwind, even more so than we do on 1-3 targets because we reach a point where we no longer use CS.
So Legion Arms really is a spam Slam/WW spec that the WOD Arms never was. WOD Arms was terrible but it was based around 20s CS windows and so it was very reliable consistent damage, the over the top Execute made for big RNG but otherwise yeah you never spammed anything, it was based on rage management and timed bursts.
As bad as it was, Legion is worse right now because you're just swimming in rage for the first 80% of a fight and you're just firing away at Slam even ignoring Mortal Strike when Shattered Defenses is not up (First MS after CS). This can be tuned out into a spec that is better than base WOD, but it's still a terrible spec and unless they make CS not important it's absolutely going to remain for the most part the spam Slam spec.
A few design changes could help Legion Arms be a really cool spec, but right now it's far from just an "OK" spec, it's as bad or in some angles worse than WOD Arms, just with infinitely more potential if they tweaked it.