A few counter points: You really cannot compare thunder to ruin. Thunder does substantially more damage for the same cast time. The dot potency is per tick, not for the entire duration of the dot.

2 or 3 whms on turn 4? Nonono. Get the raid stacked up right and use Cure III so one whm can do the same job.

Lastly, whilst yes, I'm kind of glad that overcure got changed from a guaranteed crit (As that was potentially dangerous amounts of enmity in a single cast) but it's still lacklustre at best, an end game whm on endgame content isn't ever going to be spamming Cure II, and on the few occasions where we might (A sloppily handled death sentence for example), getting a 'cheap' cure III out of the deal is going to be the last thing on our minds.