Rhino easily powers through low to mid level content with an invulnerability to crowd control and going very long periods before having to renew his ability. However, in high level content or when facing the partial backlash of a modded Ogris that blew up just a little too close, Overheat overtakes Rhino in damage mitigation.
With Redirection rank 8 and Vigor rank 5, Ember has 780 total shields. At first we will ignore health for this comparison (in most fights you try to escape before taking health damage):
Ember's effective shields are 9,286 before taking health damage. With Guardian these shields are doubled to 18,572 before taking health damage.
To compare, Rhino's Iron Skin (maxed Power Strength) will protect against 2,748 damage, then he has shields which would be 50% higher than Ember's (with equal mods) of 1,170 and doubled to 2,340 for a total of 5,088 effective shields.
Rhino would have to re-cast Iron Skin again in order to raise his protection to 7,836. He would then have to re-cast Iron Skin a third time in order to raise protection to 10,584, a fourth time to reach 13,332, a fifth time to reach 16,080, and a sixth time to reach 18,828 before finally matching the level of Ember.
Six casts of Iron Skin = 465 energy or 375 with Streamline.
One cast of Overheat = 77.5 energy or 62.5 with Streamline.
The final nail in the coffin is the fact that we haven't considered health yet. With Vitality rank 7 + Vigor, Ember has 740 health. Armor (~17.5% DR) raises that to an effective 897 health. Overheat then raises that to an effective 10,679 health. With that much effective health Ember could AFK inside a high-level Ancient's poison cloud for a minute and live to tell the tale. Just to compare, Rhino would have to cast Iron Skin an additional three times to keep up with that.
- Rhino casts Iron Skin x 9 = 697.5 energy (562.5 with Streamline).
- Ember: casts Overheat x 1 = 77.5 energy (62.5 with Streamline).
If Rhino had infinite energy he would of course be the king of tanks. But in a world where you are fighting high-level monsters that don't drop energy orbs as fast in a time when you need damage reduction the most - Ember usurps the throne as the queen of tanking.
To summarize, with Redirection rank 8, Vigor rank 5, and Vitality rank 7, Ember has 29,251 total effective health+shields. What makes this astounding is that the health orbs she picks up scale with this since her health pool isn't actually growing (it's just protecting more): in other words a health orb worth 25 health is worth 361 health to Ember. This makes pairing up with a Nekros, Mag (shield restore), or a Trinity insanely lucrative. Or just pair up with a few Medium Health Restore that you made in the dojo :)
TLDR: Overheat wins because it's more cost-effective.
This one requires a whole lot less talk. It revolves around duration and energy efficiency. With Maximized Power Strength and Maximized Power Duration and Streamline Overheat lasts for 51.4 seconds at a cost of 62.5 energy. If Blessing takes Maximized Power Duration and Maximized Power Efficiency then it lasts for 23.2 seconds at a cost of 25 energy.
Blessing only lasts a third as long as Overheat, but it provides total team immunity (including sentinels) and under half the energy. Lets compare:
- Overheat Energy Per Second = 1.21
- Blessing Energy Per Second = 1.08
Although the long duration is great, the energy efficiency of Trinity is 11% better, and when you consider she offers team + sentinel protection she'll do the better job getting your mission through a tough time unless you aren't paying attention and get killed between casts.
TLDR: Blessing wins because it's slightly more cost effective while also providing more protection than Overheat.
All in all I don't think this is overpowered.
Being able to NOT get crowd controlled is a boon, and Rhino can pull it off in a cinch. This does wonders when surrounded by lasso-happy Grineer or temper-tantrum MOA's. Or worst of all, a Napalm that just slapped you to the ground to unload fire in your rear end. All that damage can be "mitigated" simply by not being put in that situation to begin with.
Being able to make your whole team (not just yourself) invulnerable and fully healed at infinite range is also a big boon. Someone just got downed during intense combat and you need to go into the fray and revive him without him instantly dying again? Blessing to the rescue.
Most frames offer something "overpowered", and as such... they aren't. They balance each other nicely. I'm not saying abilities won't continue to be fine-tuned and tweaked by DE, but powerful maximizations such as Trinity's Blessing aren't things anyone should immediately point to and scream nerf at.