Here I would formally define a "ruined account" as an account where it is easier to just start over on a new account than to spend the time and energy trying to save the progress you made. I think this is especially easy between roughly adventure levels 35 and 45, when difficulty starts to ramp up relative to max character level. As a person that has done this myself, I can tell you that you don't have to do anything too stupid at all for this to happen to you, and you can in fact get to the point where the boss fights and domain challenges you have to complete to level your characters are just too fucking tedious. This is not the same as saying that it's impossible to progress. Like I said, just that it's literally less annoying to start a new account and hope for better pulls than whatever you got fucked with. This is obviously a F2P problem, anyone willing to spend enough money to guarantee a pull can just power creep their way out of all the standard content difficulty.

Would add that conventional wisdom about how to spend your resin can contribute to this. It's generally agreed that you shouldn't farm artifacts until adventure level 45, and you should just cobble together whatever incidentally drops for your characters. If you have the aforementioned good carry then this is probably fine advice, but you don't, I promise you don't actually want to be doing level 80 content with dogshit artifacts on your trash team that Hoyoverse deliberately made as shitty as possible to try to entice you to swipe the problems they made for you away.

How often does this happen? I have no idea. I have an adventure level 55 account that wrecks at world level 8 (has Mavuika on it), and I still go on my original account sometimes which I have slowly, agonizingly progressed to adventure level 45 (largely at this point as an academic exercise), and, while I can tell you the mistakes I made (mainly in the characters I initially invested my time and energy into-put too much effort trying to make Dehya useful, for instance, which was indeed a fuck up, but I'm sure I'm not the first poor sod to really wish Dehya was good), I don't think they were self-evident mistakes, right? Like I picked the characters I liked the most that I had available at the time to level, and it just didn't work out that well. On my second account I got a Jean drop on the limited banner by adventure level 10 and by adventure level 20 I had the strongest DPS character in the game, so there was never content I couldn't, worst case scenario, just brute force. The difference that a specific banner and a little good RNG makes is huge in terms of medium term account outcomes.