Apocalypse, Phoenix, and Garuda are valuable because with only 3 eidolons you can cover all 6 elements with a versatile passive that will remain useful at endgame. That's why they're prioritized. You might have a water team now, but at some point you could end up pulling 3 SSRs from another element. When that happens, you want an eidolon to use with them.

And as I keep repeating, Blind is a really good debuff. Most people will want Apocalypse in their main team as a secondary eidolon, and if she isn't maxed you'll suffer a stat penalty for the privilege of using that debuff.