I haven’t had a chance to jump in yet, but this is very sad to hear. I was hopeful but it seems there is simply no escaping update 25.....

Do we turn cross healing off again and see how that is? TBH with it turned back on this was never going to yield positive results. We know that AOE checks are the main culprit of the abysmal performance!! ZOS know this also. How they can come out and say that removing the cross alliance heals made no difference is insane to me. What else can be done now?

Yep, it was just was as bad as ever. I gave up in the end. I was kind of hoping it might improve performance - there were a few posts saying it was better, but half of them seem to have been written before the patch was even done. I think people are just agenda pushing again.

I'm starting to wonder if there's some weird bit of code tying itself in knots somehwere they haven't found. I don't think its cross healing - I may be wrong but I thought they'd confirmed that didn't have a performance hit. It was for "behavioural improvements," whatever that means.

It is genuinely worse than it was yesterday. At least before you could just wait til the ballgroups logged off and have a pretty fun time. Right now this game is completely dead for 3 weeks as anyone in a big fight may as well be in a ball group. It's getting embarrassing at this stage. Revert U25, nobody cares about Stadia anyway....

Need to correct myself, while the first day was fine for me, today it indeed was very laggy again. Skills not going off reliably and with typical 3 second delay.

There are a few different things here:
1. PvP is more fun. There is no more carry using the proc sets and hence the fight go according to skills.
2. Organised groups have more or less adapted to the no proc sets and accepted that they'll die more often.
3. The performance of servers feels worse than before. On day 1 it was REALLY good. No lags whatsoever even with full pop. Day 2 was very bad. Day 3(yesterday) felt even worse to me somehow. It's not fun if you get hung in the air and lag out for several seconds (like 5 seconds instead of 2 from a meteor) if hit with a knockback skill/ulti
4. After dodge rolling, I could use a few skills only after I stopped moving. I could bar swap and use other skills but some skills just refused to fire unless I stopped. Same with potions.

Overall I guess there is something else at play here. Either ZOS has increased server pop cap or reduced the processing capacity of the PvP servers. Removing proc sets should have directly impacted increase in performance which is not there. And if this premise of proc sets causing lags itself is wrong, the ZOS just need to increase the server processing capacities to MYM levels again.
Ofcourse there could be a third angle here: Proc sets removal did lower the lags but there is a memleak on the server deployment which they are cleaning up using a periodic utility and didn't really fix which is causing performance to degrade over a few minutes, come back to normal and degrade again. But in the end, 3 weeks of this is not what we expected.

Cancel the game in Europe already if you can't provide quality gaming...
Agreed with OP - performance is bad.