Judging from the dozens of Jay's live drum videos, there's a TON of push and pull in tempo so I don't think they're playing to a click unless he is really just that messy live. If it's the latter, I could understand the band being frustrated by that if the expectation is to stay on top of the click.
The font of all knowledge that is TVTropes tells me that a lot of fans were frustrated with Jay's early live performances, but that he did make a real effort to clean them up. So... I can believe it but if it's a big deal I also feel Slipknot would have cut ties a lot sooner?
I recall some rumors that he did the drumming on .5 The Gray Chapter before Jay joined. No idea is that was true but I think his playing would be a good fit. Not sure he's the type of guy to wanna throw a mask on though ha.
Adler said he left LoG because it was a toxic environment and he wanted something more fun and less pressurised. He is not joining Slipknot.
It sounds like they are playing it in full from an interview I just read. unless I miss understood what he was saying https://www.kerrang.com/slipknot-no...he-debut-record-and-potential-surprise-shows/
Slipknot is a very important band for me as a drummer who was 13 when the self-titled came out and I'd never heard such extreme performances before, but I have ALWAYS hated this way Clown speaks. It's always the most arrogant, wannabe pseudo-intellectual drivel you've ever heard. He's the guy at the party who he did shrooms once and now believes he knows what life is all about and tries to tell everyone else they don't know what they're talking about.
Per the interview, Look Outside Your Window comes out next year. He also talked a little about what happened with Jay, but it's nonsense about the band's original members going in a different direction. He does make clear that Jay didn't leave, which we all knew, but it's interesting that he makes a point of confirming that.