He didn't play a league game for them before this season.
I'm not saying that makes him a bad signing for Liverpool or Kepa a good one for Chelsea (although I do think both will succeed) and they're both, from what I gather, fine keepers, but neither has played a substantial amount of league football and neither are what I'd class as hugely experienced. Acting like Alisson is a better signing because he is substantially more established than Kepa (although I take the point about Brazil) seems awfully like trying to fit the facts to the narrative – they're both keepers being signed on talent rather than their experience.