Note - my RM is str/will, and combined with Instill/Boost, he is just one mean attacker. He's also level 37, the highest person I've seen that hasn't beaten Gey yet, with the exception of a couple people (Can't remember you all, sorry!).
My RM was like level 40 when he beat Geyzer because my connection kept dying when I found a decent party. :/
It's situational. If you have a lot of agility, you can heal people that took heavy hits at the end of the last round. If you go with a build that ignores agility, there's a chance those people would die before your turn comes.
On the other hand, if you ignore agility, you can heal people that took heavy damage at the start or the middle of the current round. With a heavy agi build, there's the chance that you'll heal people before they get seriously wounded, effectively wasting your turn that round.
It comes down to what you'd prefer: Being able to heal people at the start of a round but risk having your spell go off too soon, or being able to heal people at the end of a round but risk having a target (or targets) die before your healing occurs
If you go somewhere in the middle, then you get a mix of the pros and cons of the first two builds. Your turn usually comes around the middle, so either your healing is opportune (enough people are hurt to where its worth it) or it's even more frustratingly JUST slower than needed (someone dies the turn right before yours as opposed to several turns before yours).
Leading in to that, I can usually do some heavy damage before I have to heal.