Depends what you want or expect from an S2 I guess.
For me, it's problematic substrates such as fibreglass/resin on the Air slate. I know S2 to most people means bendy/flexible though, so in that regard Ultimate isn't in the lead.
I wasn't defending it's use for man-made quartz - I agree the water content would be a factor.
It's years since I fixed the stuff but I used old Fast-flex 2 part and more lately BAL PTB with no issues.
I just hooked onto the bit where you said it's one of the worst S2 you've used and tried to offer another opinion is all
So for me, I have a problematic substrate and think "S2" and Ultimate will likely be my first choice these days.
If I want the flexibility though, then it's BAL fastflex.