I think the HP, if Titan remains untargetable and doesn't get to keep his 90% magic reduction lol, would be fine as you wouldn't be able to reproduce Ramuh situation with a cover titan then (because he auto-covers you on summon and has hp from the start, basically front loading Earthen Armor (so he gets a different egi-2 move), it would likely be Titan has 15-25% of your max health, and doesn't 'die' at zero, rather he just has no buffer to offer, also why I mentioned the hp regeneration mechanic so titan could restore his buffer and that mechanic would have some synergy with his other skills, like his ultimate and particularly if you were in large groups). Ultimately I just want to note it's not needed in the slightest, but I would have preferred it as it helps maintain some of the old concept of "tanks" while entirely dodging Ramuh tank issues (which I understand people want to avoid, having it via this way would return it to a far more he's there for you vibe over almost like he's your pocket healer rather than tank "BUFF ME" "AGAIN".. would like it to be "yooooo, happy you're here fighting this trash with me"). All posted due to the vibe shift I don't appreciate(while I also understand we can't return to Summoner replacing tanks in dungeons, because obvious reasons lol).
By adding an mp cost, or cooldown (balance, so you can't just recast titan over and over for non-stop freebies), also sort of gives Summoner a chance to potentially weave it in for emergencies more easily than otherwise- say if you had like 5000 mp and 200 hp, raid wide is coming so you use titan which gobbles up the raid wide (and now has no hp), then shift to Ifrit. Rather than "I don't dare use, or maybe even have off cooldown, my egi-assault for earthen fury, so I'm not going to bother summoning titan anyways". Reduces the punishment of bringing him out, makes it faster (cause on summon he'll auto-cover you), and vibes towards tanking (cover) over buffing. But.. I mean you could keep the QoL and not do all the abstraction, simply make him auto-shield you lol, maybe the shield growth mechanic as well (makes him closer to a buffer again though >.>). Which again I wasn't trying to say Titan has zero use, if you get the right opportunity, haven't used your egi-assault, then 30% shield back to back is pretty good (and it does last for a while). The numbers on the shield are not bad, just not in love with the vibe and how you have to get around to using it lol. I believe there are ways, if one wanted 'tank' vibe (not to suggesting everyone cares), that would better represent tanking than what amounts to basically a support mage casting stoneskin while also not having to return to the imbalance of old (Summoner replacing tanks, or messing up mechanics because pet is targeted, and other related 'targeted' issues).
But eh, mild QoL annoyance and conceptual hang up on the shift of imagery that I don't think is quite desirable (but overall both are minor gripes, especially in light to say fixing ghosting, or improving responsiveness). Although in a general sense at any given opportunity I'd love to see each egi / demi have more flavor, over just a target type and potency shift (Titan shield and Phoenix HoT stand out of course, but more 'standing out' where balance isn't damaged would be nice).
As for the later idea-I would love playing with some level 90 mega ultimate transformation skill. I had thought Demiurge, for it's namesake relation to the demi summons, and it's own definition:
Would be fun name opportunity.a being responsible for the creation of the universe.
(in Platonic philosophy) the Maker or Creator of the world.
(in Gnosticism and other theological systems) a heavenly being, subordinate to the Supreme Being, that is considered to be the controller of the material world and antagonistic to all that is purely spiritual.
Not entirely sure where it would fit in the rotation to feel good and not feel like a weird piece to the rotation puzzle, but Summoner going "primal-like" would be neat. Could have some interesting modifications to the mage rotation side of the job without causing a new sort of chaos lol (like how phoenix works).