Titan has never been that great, he can't hold hate off you unless you hold back and if he dies he's never getting hate back and the removal of sustain was just the last nail in his coffin.
So, I think it's time for some adjustment to Titan and/or the summoner.
If smn can't heal then there's simply no point in having a tank pet, he could be the best tank in the world and it won't mean squat if he dies. So before adjusting Titan, smn needs adjustment. Make physick scale off INT on smn the same way DoTs scale off MND on sch and add the effect of sustain when used on a pet. This alone would be enough healing to keep Titan, or any pet, alive while also making an utterly useless ability on smn have a purpose.
Now on to Titan himself. First off, his rock buster should generate more enmity, at current levels I rip hate off of him as soon as I enter dreadwyrm trance, he was fine when we were just a DoT mage, but not anymore.
Also, his cooldowns are all way too long. 15s for his AoE? 120s for low mitigation?
His AoE should have a 3s cooldown, it's his equivalent of unleash or overpower, he should be able to spam it. And 120s for a 20% damage reduction? Rampart on actual tanks is only 90s and they have other cooldowns to back it up! This should be 30s at most.
As for landslide, I don't think Titan really needs this, if we want to stun we have ifrit, what Titan really needs is a provoke. Change the effect of landslide to provoke or ultimatum so if he dies we can resummon him and he can actually take hate back.
With these changes Titan would actually be able to serve his purpose and the smn would be able to keep him alive to serve his purpose.
But, assuming SE is adamant about this no pet healing path they've chosen, I simply don't think there's any point in keeping Titan as a tank, in this case, I think Titan should be made the "AoE pet".
Remove rock buster and replace it with mountain buster as his basic attack, change earthen ward to a 10% damage reduction for the party, make landslide a frontal AoE similar to doom spike on drg and add tumult which will be an AoE attack with an additional effect of draw in to gather mobs up.
This would make Titan great for dungeon trash pulls and would make up a bit of the loss from the bane nerf at lower levels.