Why would you play your Eternity so early?
Yes, that's basically exactly what I just said; I wouldn't play an Eternity until endgame by which point making such a play would be extremely risky.
If Eternity comes out you can just Endow that one before playing Pulverizer.
Unfortunately that would also mean that no creatures would be available with Steal or Destroy as an ability which I generally find exceptionally useful in Timebows.
Endow your Pulverizer.
If you're relying on mutants to destroy stuff for you, you're relying on TWO rolls of the dice instead of one - first getting Druid early, then getting a lucky mutant early.
Okay, let's compare the scenarios then. First scenario is the one you just described. Second is:
1) Drawing an Eternity early enough, drawing a Pulverizer early enough, hoping you get a Crusader from Rewinding a Skeleton. THREE dice rolls instead of 2. -OR-
2) Drawing a Pulverizer early enough, and drawing a Crusader early enough. 2 Dice Rolls for this one too. While this is a possibility...the damage potential provided by Fallen Druid is much greater than a single Crusader. Also, let's not forget that, as you said, by using this method you would be wanting to save Eternity until late game, no? In that case you would need to spend ~21 turns Rewinding creatures to get the same damage potential as a Fallen Druid and you would have to stop as soon as you came close to decking out. Druid can continue to be used even after this point and it usually needs to be used after this point; also, this generally means that your duels will take longer than they have already. For Rainbows running Elite Queens, this tactic will reduce possibilities greatly.
In my experience running timebows, novabows, CCYB, etc., mutants with destroy never made a difference. They always came so late that I already had control of the game, or they came early but were either useless or got incapacitated right away.
The one exception that comes to mind is the Light Pillars several FGs use to power Miracles; destroy/steal mutants can speed that denial up. But that's just a speed change, since if you're worrying about Miracles, you're headed toward a win.
As an aside: A CCYB variation using Mutations sounds very interesting.
Again, as I was only discussing Timebows, this is what I was saying from the beginning. Is Druid absolutely needed for you to win? No. Does it increase your win rate/speed? Yes. Do people usually like to defeat FGs quickly while maintaining good win rate? Yes. Therefore should Skeleton's buff make Druid totally worth replacing? No.