I've seen people stack medica 2 and regen for the sole purpose of buffering the tank during wall pulls in most of the expert dungeons. It's one of those things that sounds like a good idea because hypothetically the tank is going to take hits when the mobs surround him and therefore the ticks would heal, but it completely misses the fact that half the healing from the spell is immediate and the other half is the regeneration. It's not the same kind of deal that they get with the Regen where all the healing is from the regeneration and therefore is delayed.
The other problem with medica 2 is that the regeneration doesn't last that long and most likely the tank is going to have their own rotation either applying mitigation, self healing, a shield, or some mix of the three. So truth be told a whm should never use medica 2 unless they are healing the entire group in response to an AOE attack, and they should also only use medica 2 if the group is going to be too spread out for the cure III as both are 0 MP to cast thanks to the extra skill they got to make the next cast cost nothing.
The original design for medica 2 was built for a game where they didn't precisely build the fights out and was supposed to be a compromise for greater range, but in the new version of the game it now serves to mostly counter bleed effects on the group and to buy time to use something else to heal the group. Cure and Cure II were also from a time when MP and TP were primary resources and casters were expected to take time to actually heal someone and it was more firehose healing. Cure I was the efficient heal that was combo'ed with regen, and Cure II was for emergency casts and get a free cast proc to assist the WHM keeping the main tank up. Additionally, Aero I and Aero II were two completely different spells and Aero II was an AOE dot, not just an upgraded Aero I.
They definitely need a new naming convention for the spells in this game but I doubt they are going to redo it. BLM has the problem of Thunder I and Thunder III being single target and Thunder II and Thunder IV being AOEs, yet Fire I, Fire III, and Fire IV are single target with Fire II being multi-target, and Blizzard I, III, and IV being single target while Blizzard II is an AOE.
WHM has Cure I and Cure II being single target and serving different purposes early game, then Cure I becomes redundant after MP management improves and Cure II becomes a strict upgrade, while Cure III is a targeted AOE and anyone who isn't familiar with FFXIV would logically assume it is an upgrade to Cure II, which it isn't. And this isn't even going into the problem of having the Lilies added later on with the caster only getting the single target lily and no payoff for ages.
WHM isn't even playing the same game at sub 50 that the post 50 WHM is playing, and that goes for a LOT of the jobs.
It's pretty impressive what the devs have done to change things and try to get these ancient relics working with the current game.