The OP asked if OLED Burn-In is a Big Problem. Imo, it is a big problem for anyone who just wants to watch TV as it's been done since televisions arrived in households decades ago. We didn't need applied science degrees to watch TV. We didn't need education on which channels we could watch and which would increase our chances of destroying the TV based on what our neighbors revealed happened to them. We didn't fight over which seat provided the only premium experience. We simply put the TV where it fit the best not where it had to go or it wouldn't work. We didn't have to worry if the drapes were open or closed much less a dark environment like a light free basement. We didn't have to make sure an auto fix was implemented every time we were done watching something and hope the fixing was indeed fixing. We weren't limited to how long we watched the same thing continuously or forced to watch other things we don't like too. We didn't have to inquire from our neighbors to make sure we were watching TV correctly for fear of destroying our TV. There are expert TV watchers who find much of this perfectly normal today though.
Often these expert TV watchers dictate that watching the program you like is not only bad for the TV, but bad for you. Therefore, save the TV from breaking and only watch what the experts watch because what you want to watch is wrong and so is how you watch it. This applies to many things in todays age: That game you like - sorry, it's on the no can do list. That TV show you like - nope, it's forbidden too. Your TV as computer monitor - are you out of your mind? You want to binge watch what? - don't you know you have to change programing on regular basis? Wudda' you mean the picture is too dark? - move it into a black hole where it belongs and it'll look bright enough to burn your retinas out. The TV is off limits but me and the kids want to use it but you have to be present? - yes, you guys are not expert TV watchers and I am so I'll look after the TV to make sure you guys use it correctly and then there won't be any problems... maybe. Etc.
When the avenues are exhausted and experts and non-experts alike put their foot down and say enough is enough, I just want to use a TV any way I see fit, the replies are always the same: You broke your TV because you are not an expert TV watcher. OLED's do not burn-in all by themselves. You did it. Buy a cheap LCD then and watch your garbage on garbage. Or as recently analogized, use a BMW OLED for special occasions and use a beater for your daily driver. I find this humorous. In other words, buy a $5000 OLED for occasional use and buy $300 LCD for everyday use. You'll still need to learn the do's and don'ts of your OLED. Just because it's used less than your LCD doesn't make it less susceptible to destruction. But assuming you've taught yourself how to expertly watch an OLED on special occasions, did you really need to? The experts have us brain washed that no other TV is going to look as good. For us non-experts, is that really true? Are we even going to notice what you notice? I don't think so. You know why? Because experts are watching their TV instead of the content just like audiophiles listen to their equipment instead of the music. They often wave papers and websites around saying 'see it says so right here'.
That said, for the majority, if you put a cheap $300 LCD (as suggested) next to a $5000 OLED the difference will be dramatic. If you put a $5000 LCD next to a $5000 OLED (or any fair comparison) the only differences you would SEE is those the OLED doesn't do too well at. Burn-in being one of the primary downfalls and prevention for it leads to further caveats and special usage scenarios only. Sure, an LCD has some MINOR picture differences an OLED doesn't and vice versa. These are always overblown one way or the other. So, imo, why on earth purchase the new guy on the block that limits your usage and also the possibility of burning in a static image ruining the panel when you could use a different TV any way you like just as you always have, that also produces an exceptional quality picture. Just because a tech is newer doesn't make it better. Imo, it's just different and with that difference comes problems older reliable tech simply doesn't have. Burn-in being the 'biggy'.