I recently changed my personal email. Updated every account I knew of (thanks Bitwarden!!). Updated about 120 accounts, closed maybe 20, and 5 or so can’t be changed.
Of the ~120 that I changed, I think about half of them were easy to change. Not much confusion. There was a clear enough process. Etc. Most of the rest were difficult to change but I could do so on my own eventually.
Something like ~10 accounts required emails and phone calls to support.
A few were terrible. Things like updating my email address in 10 places for one account. Or the updates go fine but just didn’t work, requiring many repeat attempts or phone calls.
So it’s a real problem in my experience. But not the norm. Maybe 1/10 rather than 9/10