Ahriman
Tyrant
I agree with Ahriman on late religions and their relative lack of power currently--Quizarate in particular, since Golden Path just gives happiness (who needs it when you should already have a big empire with lots of happiness resources) and negative science.
I think the solution here is to make happy and health harder to get, so that Golden Path *is* really valuable.
The other benefit though of Quizarate obviously is for a religious victory, as it wipes all other religions when you expand it.
Is it possible to introduce a tech (or maybe give fanaticism that role) that specifically allows you to adopt a state religion; i.e. at default you cannot have a state religion?
Well, its possible to make it happen with a civic change; the default government civic for eg could prohibit a state religion, while all others allowed it.
I don't support this, I'm just saying its technically feasible.
But the culture and happy advantage from an early game religion is also nontrivial.
Besides, in the early game before they have Fanaticism, there isn't any significant trade with other civs anyway. So what difference would it make?
I'm not convinced that Tleilaxu are underpowered. But if they are, I don't think that reducing their xenophobia is they way to fix it, I'd tweak their other stuff. Like increasing facedancer power (lower EP cost for missions?) and maybe changing how gholas work and/or bringing them earlier.