Now that scorches passive received the armor reduction buff at lvl 40 he's much more useful compared to his lvl 30 self. I use him during boss fights where he's only got one target to worry about and the speed helps my warrior get out of danger while giving squishes that lil extra help with the shield.

He's still a marginal mythic pet at best though. He either needs to do a bit more with his happiness bonus (damage reduction or Dodge) or do more with his arcane (stronger party buffs or better shield).

As for haze and shadowlurk, they are definitely worth the 90 plat along with their other 90 plat counterparts.