I’ve never had any qualms about dining alone and I’ve doing it for 50 years. Sure every now and again you get that haughty treatment but I don’t let it bother me. It usually doesn’t last once I’ve told the manager the waiter isn’t providing good service and if he/she expects a good tip it had better improve. This has been rare.
Also I tend to order a good bottle of wine. When the server sees that things are usually fine.
There have been a few times when I wasn’t seated at all. Obviously I never went back and wrote up very bad reviews. But honestly things are usually fine if you make your expectations known and treat the staff with respect.