Short answer: it depends.
Short but useful answer: it depends on if your religion benefits from believers in other civs.
Medium length answer: it depends on if you gain anything from believers in other civs. Whether it's worth doing or not at that time will depend on how late they are to the religion game. If you suspect they'll have their own religion soon and yours will get pushed out, it's probably not worth it. If you're quite fast at religion and they're very late, you cAn almost ignore the pantheon.
Long answer: too complex to type on phone. Factors include relative times of founding, what's in it for you, third parties, city placements, and diplomacy.
Which difficult level ?
I know in general it seems a waste to spread a religion to a civ that has another religion. It seems they keep switching it back to their religion. Is it the same with those states that have lightning bolt symbol? A pantheon?
one time I had five cities in a remote area far enough away from other civs and myself so they stayed atheist for a very long time. I finally sent a GP to bring them into the religion and also I had the one hundred gold initiation enhancement. It took the GP two tries before he was able to turn the largest city.
"Always" clearly isn't a good word to use. When we add up things like the "Just War" enhance belief, the ones you list, and others, we'll end up with a list of exceptions.Unless you have faith to burn: It's always a waste to use Missionaries / Great Prophets to spread your religion outside your territory. (Unless you get a one time bonus that turn such as a city state request or the Initiation Rites belief)
Yes, IMO.
Because if you won't, someone will do and they will also spam prophets or missioners for that religion. So, spread your religion as soon as possible to any cities which hasn't Religion. No matter if they have pantheon or not.
The AI doesn't care if someone has spread their religion or not; they'll send their Great Phophets to convert it either way.
In fact multiple AIs will be doing this; so you'd be fighting multiple civs Great Prophets).
Meanwhile another AI will notice the lack of Inquistors in your territory and send Great Prophets to your home territory while your fighting the other ones for religious supremacy in someone elses land.
Yes, yoyou're right. But if you convert another civ first, you have advantage in "convert battle"