Parmandur
Book-Friend, he/him
True, you're right but it really ends up undermining other characters due to the fact that DC creep means there's no point for them even trying things after a while, which I think is really problematic.
I would have been much happier if they'd done something like having Expertise grant automatic advantage on checks, some number of rerolls, or rolling D10+10 instead of a D20. That way the overall bonus wouldn't get so high but the character would be able to perform more reliably. This would reinforce just how insanely difficult achieving DC 25 or 30 is even for highly proficient characters.
IMO fearing multiple advantage (roll three take the better of them) isn't really worthwhile. The effect on the expected value isn't that huge and diminishes but it represents just how much more reliable a character with advantage is compared to one without.
I think that skill proficiency could well have worked with advantage instead of there being a flat bonus. WotC's big mistake when they implemented bounded accuracy for skills and saves was not to have an analog of hit points (i.e., requiring multiple successful rolls to complete many tasks) and relying on high static modifiers.
They wanted Proficiency to be a dice pool system (which they did put in the DMG as a variant rule). Expertise adds another die to the pool in that set-up. This I like.