This has probably been said a thousand times but once you know mechanics all that is left is the dps check. Therefore dps get priority on the gear. The only way it would switch is if there were sections that were impossible to get through without more healer or tank gear.
The reality is that heal checks can easily be handled by healer’s overbloated healing kits (healers actually have so much downtime they’ll be dpsing 70+% of the time, not just “one or two” spells). And tank busters are easily mitigated enough to no be fatal even when you’re way bellow the minimum ilvl.
Either passing the dps check or minimizing the amount of mechanics to handle are therefore going to be the main priority.
It also doesn’t help that historically tenacity usually hasn’t benefitted tanks enough to be worth its cost in dps.
