Slightly more common, proportionally, than ringed Earth-likes. Much more common in absolute magnitude, though, as WWs are ten times more common than ELWs. I suspect the reason for the higher proportion of WWs with rings is that rings are more likely to be generated around larger planets, and Water Worlds have a much higher upper mass limit than Earth-likes do.
Logically, yes, though perhaps slightly higher as Terraformable WWs can go heavier than actual ELWs - all the way up to 1.99 surface gravities, whereas ELWs tend not to form above 1.6 gravities.