To chime in with another single data point, my experience with Azure support has actually been pretty good. Tickets take anywhere between 2h and 72h to get a response, which I'll grant is not ideal, but the ticket handlers I've dealt with have all been knowledgeable and helpful.

I work for enterprise-level companies though, so I don't know if support varies for smaller ones depending on spend.

That's on point, I used the Azure platform for around two weeks to see if it would be worth for our company to move to it and my account got randomly banned, no answer from support except that they don't want to say why. I'd not trust Azure to put anything important on it based on my past experience.

I work in a SaaS company, and we run "a lot of Azure". We open around a dozen tickets annually. The response is a mixed bag. The response times are pretty good, but it depends what will you get as a response. Sometimes you get asked a bunch of irrelevant questions just to get a simple answer (which actually helps). Sometimes you just can't get them on the same page. There are support engineers that just do not know what are you talking about. Typical example: snapshots. It took me once like 10 emails to clarify that I'm having issues with managed disk snapshots, not with blob snapshots. At the end I'm not even sure he was still aware what am I asking, the guy was completely oblivious. He finally sent me some screenshot of his own control panel (where he sees much more info than the user does), to show me something, where I actually noticed something else that unstuck me. But if he didn't we would still be sending mails back and forward.

Is Azure unique in that if you shift to Azure you cannot also use other cloud providers but if you are on GCP or Azure you can use the other?

Azure and GCP had either comparable or worse UIs for a lot of services compared to AWS, but region specific UIs were a notable unintuitive design compared to others.