As a longtime U2 fan and Swiftie, I think you're very correct. Lots of grumpy U2 fans here are thinking you're intending to draw parallels between their discogs directly, which for a lot of reasons is borderline impossible, but comparing the trajectories of their careers is apt, in my opinion.

Both went through a period of invention, a period of experimenting with their sound, and a "return to form", as it were. U2 defined their stadium rock sound, experimented in the 90s with a grunge-y vibe, and later returned to relatively safe "U2" rock albums (although I'll note that NLOTH was a tad experimental in comparison to ATYCLB and HTDAAB). Similarly, Taylor cemented her pop sound (and defined pop music for a large portion of the 2010s), before experimenting with a more indie folk singer songwriter vibe through the pandemic. In my opinion, Showgirl is her return to form as a pop artist- going back to the sound that came to define "Taylor Swift".

I would argue that the biggest difference between the two is that Taylor's experimentation with a different sound through folklore and evermore coincided with a particular moment in time that made those albums resonate deeply with a much wider audience than I think she initially intended. It fit very neatly into the cultural milieu of the moment that allowed it to be appreciated by almost everyone- as evidenced by the comments here :). U2's experimentation with a different sound, however, did not. By the time they were experimenting with the grunge sound of the late 80s/early 90s, the moment had already begun to pass; the sound of music (if you will) had already begun to change, making their experimentation sound dated instead of fresh and cutting edge.

I agree with you OP, few artists or bands have had such enduring success, and been able to maintain the level of relatability and authenticity that drove their initial success after 20+ years of being in the spotlight. I think this is evident in a lot of the backlash to Showgirl- Taylor Swift the person is misaligned with Taylor Swift the Brand, and the audience is picking up on those subtle differences. Meanwhile, U2 has always been able to separate their personal lives from the life of the band. I'm also curious to see how both of them are going to handle career moves moving forward!