I haven't had many battles with them, but in every match involving a dynamo except for one, it lost the match. When I was against it, I could actually approach, and splat them as it was intended. No more weird laggy swings, no more trades that feel like I should have won, it feels right. For better or for worse (let's be real, it's for worse regarding the weapon itself), it was remade to function as the devs originally intended. A slow, heavy, long range roller that guzzled ink. And from what I can tell, that's a really bad weapon idea when put into practice.
Either way, I think the game is much more fun and healthier without the Splatoon 1 dynamos. Call me salty and bitter, but they were just broken in the first game for anyone not using a super long range weapon. The devs probably looked at the feedback and play data of the first game, and they knew they could not let the Splatoon 1 dynamo return.