8 and 10. 8 is the MINIMUM number of party mits that you'll bring between 6 non-healer players in a standard full party. 10 is the MAXIMUM number of party mits you can bring between 2 healers. For reference, here's said party comp so you can count it yourself.
WAR/GNB/SAM/DRG/BRD/BLM
WAR - Reprisal + Shake - 2
GNB - Reprisal + HoL - 2
SAM - Feint - 1
DRG - Feint - 1
BRD - Troub - 1
BLM - Addle - 1
= 8
SGE/SCH
SGE - Kera + ZoeEuProg + Holos + Panhaima - 4
SCH - SS + Deploy + Fey Illum + Expedient + Seraph - 5
+ 1 for on demand shields
= 10
We can debate the value of individual buttons, but that's beside the point. This is where the core of the healer problem lies. No matter how much you increase heal checks by, every healing check is a mitigation check, and half the responsibility for that lies with everyone but the healers, unless you want every heal check to be fixed damage that ignores shields, but then things get boring quickly for different reasons.
Understandably, tanks and DPS don't want to be completely beholden to healers for their own survival, so I propose the following. Change the DPS and tank generic party mitigation tools to personals, then spread the lost party mitigation among the healers. It leaves DPS and tanks with some agency while not stripping healers of their's. This will return the role of keeping the party alive to the healers, giving them back their much needed identity. The following abilities should be changed to personal mitigations on tanks and DPS, the specifics of them is irrelevant to this post.
Reprisal, Shake It Off, Divine Veil, Heart of Light, Dark Missionary, Feint, Addle, Troubadour, Shield Samba, Tactician
This leaves flavor abilities like Passage of Arms, Dismantle and Magick Barrier, as the devs already don't balance mit checks with these in mind. It keeps the flavor on the respective jobs and arguably enhances it by limiting the number of non-healers that have party support.
Next for how to re-implement the lost mitigation on healers, I'd say it's best to keep things simple and avoid any complete reworks while minimising new buttons. I'll outline that in the next post as I'm at the character limit.