Maybe if you started doing it when they were kittens they might accept it more easily. But I doubt it. I think it's more a question of dignity than discomfort.

But there are times when a cat harness is the only way to cope with a situation.   Just don't expect to be loved for it by the cat, and mind those teeth and claws.

And there are of course some cats who don't seem to mind. Maybe they heard some wiseacre saying what I said just there, and decided to show them up.

Perhaps putting on the harness without the lead to start up with might be a good way to do it.