I think Poptimism wasn't a terrible phenomenon; but like all trends it was overdone. In essence it wasn't hugely different to the same "stop being so up yourselves" reaction that led to grunge and punk (people forget that early 60's girl groups were big influences on those genres that reacted against more pompous and self-important genres). Like all such tendencies it eventually crests and is beginning to hit its ow backlash.
There is a direct genealogical line between the "don't bore us; skip to the chorus" ethos of early-60s Brill Building confections and that of the Sex Pistols or the Ramones.
The pop-crossover dominance wasn't/isn't
artistically terrible, at least not inherently, but I agree with BRTD and Xahar that the reasons why it caught on are dismaying.
Most of the new music I listen to is downbeat "girly" art pop like Florence and the Machine or Phoebe Bridgers. Many such acts are technically still classified as indie rock by some people. I like Taylor Swift for generational reasons so I was really excited when she started making that kind of music a year or two ago.