Yes, that's one of Christianity's less attractive aspects in my opinion.
I don't really have much problem with other people believing those kind of things, provided that they keep their personal beliefs out of my face.
As for me, I don't think that all religions have the same goal. Some of them aren't about moving to some wonderful paradisical place in the sky after we die. Some aren't focused on being 'paths to God' at all. (Historically, not all religions have been monotheist in quite that way.) If religious participants can have different goals and purposes when practicing their religion, then it's reasonable to assume that there can be more than one religious path.
I suppose that it's possible to argue that religions in general all point people towards some ineffable psychological state that we call 'spirituality' or whatever. It's hard to describe but many of us can recognize it when we encounter it. And I think that it's undeniable that adherents of very different traditions can all display it, despite their believing in very different doctrines.
I have to say that I'm viscerally put off by Islam, but that being said, some of the most 'spiritual' people what I've ever met were Muslim Sufis. I've encountered it in some (not all) Buddhist monks, in Catholic contemplatives, in representatives of a whole variety of traditions.
Yes, I'm with you there. The ones who wear their "tolerance" on their sleeves are often the least tolerant people imaginable.
I suspect that we might disagree there. It's true that faith in Jesus is probably the only way to be saved by Jesus and receive whatever the payoff of that rather Protestant-style Christianity is supposed to be. But that's all relative to one's belief in that sort of Christian religious doctrine.
Somebody practicing Zen might adhere to a radically different belief system and might have very different goals in mind when engaging in his/her own religious practice. And practicing Zen in the traditional way might indeed be the best path to realizing the goals of Zen (assuming that Zen even has goals).
I'm inclined to think that they are all 'signposts' as you put it, but that they don't necessarily all have the same goal. I think that each of them can arguably be true in its own context, hence the relativism that I expect that you reject.
I am inclined to suspect that reality is indeed one and that there's some underlying psychological state that many/most/all of the religious traditions are reaching towards and want to maximize regarding our relationship with that fundamental reality, but I don't actually know this. So to that extent I have some sympathy with the 'perennial philosophy' ideas. I like them, but can't say that I fully believe all of the things said by champions of this sort of philosophy.
Perennial philosophy - Wikipedia