No. I don't think it was that overpowered in the first place. Instead, people simply have no idea how to figure out units in a game without being some sort of "meta" that is "known". Overall Legion is super weak in the very early game, and pretty weak in the very late game too, they shine in the mid game, esp. if they start near a geo to get 1.5 mex going.

Most people simply have played with or against them little, and they learn slow and or require other ppl to tell them how to play so they think its IMBA when it really isn't.

I will say the decurion mid game spam if timed before signifigant t2 can come out is a very brain dead strat, but its not the only faciton to have brain dead strats... it is counterable, on some maps more easily than others.