I vented my spleen about this recently as well ... just not so eloquently — you can read it here, if you've got nothing better to do (trust me though, you have)..
But, yeah ... although I gave myself a shake, quit my pitiful whining about First World problems, pulled myself together and got over myself ... I know what you mean — Medium has long been inducing a sense of ennui in me for the same reasons you state here ... but I just can't find another platform with suitable reach or even the pathetic featureset.
I'd go back to LiveJournal, but I don't know I'd be confident it weren't too risky opening up my browser to the hosting service with all its weird and wonderful advertisng (malvertisng?), so I'm caught between a rock and a hard place ... wanting to leave, but unable to find anywhere to go *sigh*
Whether my 'best work' (if I have sufficient delusions of adequacy to even call it that) is long since behind me or not (I suspect it is, tbh), however ... my heart's just not really here any more.