Your numbers on inner beast heals are way overblown.

Secondly yes thrill of battle and inner-beast will allow you to take a few hits, but the healers have to scramble to top off your health whereas a PLD can just use a cooldown and make healing a lot easier to manage. This matters because people other than the tank will need heals and there are many boss mechanics in coil which require a healer to move or dodge causing an interruption in healing.

What you are describing throughout this thread is the ability to self-heal / thrill of battle through a few boss attacks. Late coil bosses hit extremely hard a lot more quickly than you will be able to self-heal or use thrill of battle.