MP was never a issue with SMN imo.
and well, on lv90 gear crit is pretty high.
AND you get burst damage, that is the only issue smn has now.
We are talinkg about 2 (TWO) Ruin II instead of 1 Thunder.
You won't have issues with MP.
I said "spam", true, but it's not really spamming. It's just using it once or twice depending on your DoT timer.