Physick is too weak for lvl 60 casters?

[Saggo]

Except Titan wasn't built with Tanking anything that hits much harder than a regular mob. His entire purpose is to keep things from hitting you in Solo.
He can easily Tank FATE mobs provided you're not in a zerged FATE that scaled the damage up too high. At that point, even real tanks struggle without a Healer.
The only argument you really have is that perhaps Sustain needs a tweak for lvl 50+, but I'm not sure how well his HP scaled.

Well no, that's not true. Most 1-49 content he did just fine on bosses, a lot of dungeon bosses too. At 50, he could tank just fine most FATEs. I mean, I saw it, I was there. It was slower and less efficient, but it was fine. The FATEs Titan struggled at were obvious group efforts like big ones at the end of FATE chains. SE seemed to think it was fine too, since for a nominal DPS loss you got a functioning tank.

We could say "Titan was for trash only" all we want, but with no official statement, that's not what experience shows.

Obviously, this was different for endgame dungeons and trials, and like I said, most people didn't expect or care for Titan to shine there.

Come HW, 50-59 leveling content, he gets wrecked by scaling, hard. Damage scaling far outpaces the Titan's HP (since it's tied to caster gear VIT), which ruins his viability as a tanking pet. And since Sustain is HP% and a HoT, it can't, pun not intended, sustain Titan.

You want to tweak Sustain, but for it to be a viable it would need to be on the order of 15-20% of Titan's HP a tick in order to keep up with damage. It's actually more balanced to improve Physick's effect on Titan than it is to supercharge Sustain.