If you’re a tanker, you should usually have enough mitigation to out-regenerate most threats automatically unless you’re using a click-reliant set like Bio or Rad.
If you’re an invuln or SR tanker and you find yourself needing more mitigation often, it’s your build that needs work. The fact that you think you need heals just tells me you haven’t gotten good enough mitigation yet.
My SR tankers have capped defense, capped DDR, capped resistances once at low health, and higher than normal HP and regen. I don’t need heals because enemies just plain don’t hurt me faster than I regenerate once I’ve got scaled resistances kicking in.
Endurance on the other hand is a major pickle. You can beat it without Ageless, but, in most circumstances, why bother? I’d just take Ageless anyway because you shouldn’t need any other Destiny on most tanks and Ageless boosts your offense. And submitting to relying on Ageless for endurance frees you up to focus more of your IO’s on offense. Most of my tankers have Ageless. Even the ones with good endurance tend to go Ageless - just Ageless Radial for the DDR if they’re already good on end. My WP tank and my Ice tank have Ageless Radial, for instance.
I have a completed tanker with every primary plus 2 Darks and 2 SR’s. They’re all good enough for me. HMU about any of them 🙂