Makes me wonder if one used dark mode, or reduced brightness for in Windows use, if burnin could be prevented. Since Inknow TVs reduce brightness on channel logos to prevent burnin. Plus pixel shifting is more efficient if it isn't nice bright static line. Dunno if this monitor uses it. Finally screensaver will only help if you are AFK for long time, it won't fix the issue if you got Chrome open and are actively working for hours because I'm that case it won't really engage it. But so far burnin wasn't really solved, we only added mitigation techniques to work around the issue, which isn't solution, it just reduces chance if it occuring in certain scenarios. Hence why I would never take OLED as work monitor. Gaming sure, bit even then if you play one game all the time you are likely to see UI burnin, if it is using too bright static elements.
As for whole warranty, I don't think Dell resolves any burnin issues. They knew people won't buy them if there is no warranty since they knew burnin is big issue. So long burnin warranty is likely there more as bluff in hopes that not too many people notice burnin, to help with sales. It is a gamble, but then again big corporations are known to jump on quick cash grabs without thinking about long term consequences, because it allows them to tell shareholders how they are successful today. They much more rarely go opposite and try to convince shareholders that something is good for long term. They just leave long term to be problem of whoever will be in position at that time, even if they risk it being themselves or just along the way find way to turn numbers around and hide the issue or shift blame.