In competitive play, Electric-type Pokemon becoming immune to Thunder Wave barely left a dent in the move's popularity at all -- I'd say its overall effect was more of a buff for Electric-type Pokemon than it was a nerf to the move or to paralysis itself. Though Thunder Wave did become less difficult to deal with after the Gen 6 paralysis change, the move remained extremely popular as it continued to provide a way to immediately shut down set-up sweeper Pokemon, slow down Pokemon and put players at a significant advantage against the paralysed Pokemon. I would go so far as to say that, along with Knock Off, Stealth Rock and Scald, Thunder Wave was one of the most effective moves in the entire competitive game in the last generation (and in many before it). Its utility was virtually unparalleled; even if Electric- and Ground-type Pokemon could switch into it, that's still sixteen of eighteen types of Pokemon that do not want to have their speed reduced 75% and have a 25% of having each move fail. Perhaps that typing analogy is oversimplified, but the point is that the move was still crippling to the vast majority of Pokemon in the game and was consequentially a toxic move to the metagame. Imagine if there was an attacking move that was super effective on sixteen of eighteen types? Again, oversimplified, but Thunder Wave's effect is "super effective" in and of itself, wouldn't you say?
I am definitely of the belief that what was done in Gen 6 was not enough to properly address Thunder Wave and paralysis in general as an issue in the game; hopefully the above was sufficient reasoning as to why I think that. I sympathise with the developers in wanting to "nerf" the move again -- mechanically, paralysis borderlines on being uncompetitive as it punishes players at no particular fault of their own. The change that was made, reducing the move's accuracy by 10%, I think was a warranted change to the move to help stop it from almost being a crutch for some teams to deal with certain set-up sweepers -- hell I'd even argue certain Pokemon (Klefki) are only popular due to their access to Prankster Thunder Wave and the sheer utility that provides. Paralysis itself was also nerfed a second time in Gen 7; now Pokemon's Speed will be 50% instead of 25% under paralysis, which I also think was a good decision as it should help prevent paralysed Pokemon from being almost permanently stuck moving last. (Which, note, I do believe can have a place in the competitive game, but Thunder Wave's take on it is just too powerful and too risk-free as it stands with all the extra effects it has.)
Perhaps the change is hindering Thunder Wave's helpfulness in-game as a means of applying status conditions for capturing Pokemon, but the move is still fundamentally the same and continues to provide the same capability as before -- just not in a way that is as debilitating to the Pokemon it effects as it was previously. Perhaps the move's being "fundamentally the same" is part of the problem; even after these changes, I highly doubt that Thunder Wave will cease to be popular. It's still the same move, just not as reliable and a bit more punishing. I think the change was in the best interest in the balance of competitive play in general; this second nerf is only a problem to me if the move falls away completely, and I certainly don't see that happening at all. If anything, I'd say the changes were were undershot, because Thunder Wave is still going to be quite difficult to deal with in competitive play as there are still few ways of guaranteeing a way of avoiding the move.
tl;dr: Gen 6 nerfs hardly affected Thunder Wave or paralysis as a whole, Gen 7 changes were therefore warranted and are a step in the right direction for balancing the move in competitive play.
