Granted power draft #2 works for me if you don't feel it's too vague about what constitutes a "worm." I think it should be ok to leave that to DM's discretion.
Yes, the phrasing needs a bit of polishing as to what constitutes a Magical Beast "worm". How about:
Granted Power #3: Rebuke or command worms as an evil cleric rebukes or commands undead (only affects vermin and magical beasts with Intelligence 0 or 1, what counts as a "worm" is at the DM's discretion).
Use this ability a total number of times per day equal to 3 + Charisma modifier.
Earthquake works at 8th level. I also like worm tell at 6th level, but you have footnotes 1 and 2 reversed (I hope ).
Huh, I just noticed that myself. Easy enough to fix as I update the Worm Domain Working Draft.