Depends on the individual. A small/struggling PR agency will take on a reputedly nightmare client if they're desperate for revenue - God knows I've had to do that at certain points. And, the H&M brand might be kryptonite amongst the glitterati of California, but they're still globally (in)famous, so it's not necessarily always a bad thing to have on your creds docs.
Good agencies with a healthy P&L can absolutely afford to turn down clients - I don't think H&M will ever work with someone on the level of Sunshine Sachs again.
The same goes for individuals. I have never heard of any of the 'new court' that was declared with such fanfare the other week, but they all look very young to me - personally I wouldn't want anyone under about, say, 45 running my PR strategy if I was globally famous. You need a few grey hairs, someone with hard-won experience. An older person to drive strategy; the youngsters on the team to run tactics and execute.
I also wouldn't discount the effect that the dawn of AI is already having on the more commoditised sectors of the PR industry (to which social media PR is especially vulnerable). Some people just really need a job.
I don't think H&M pay big bucks because I believe the rumours I keep hearing about their cashflow situation, which is allegedly becoming quite critical. I've just heard the same things from too many different, respectable sources to not believe it.
And, yes, I'm sure there are some people who genuinely think they can make a difference, that they'll succeed where others have failed, yada yada yada. When you're young, you tend to have that sort of professional arrogance. If you're anything like me, you get disabused of it pretty damn quickly.