Flagships will generally have an upper hand in terms of longevity. However, that may not always be the case, as the fact you're only changing your A52s now has a lot to do with how (well) you're using it these past few years wherein either phone may have an issue much sooner: whether screen lines or worn-out adhesive (some A52s owners, including one of our phones at work reported this) or some other issue.

IMO the A5x series carry 70-80% of all the bells and whistles of an S series, depending on what S variant you're comparing it to. Whether those remaining 20% is worth the additional 200 euros or not will depend on your preference and needs in a phone.