What Jeremy Crawfords comments mean in terms of changes to the game?

No two parties are the same and no two encounters are really going to be the same, so any published encounter as is is pretty much calibrated for some nebulously defined average group of PCs that will never be the actual party a DM runs an adventure for. Looking at the encounters in a module beforehand and checking if they need to be tweaked a bit should arguably be standard operating procedure. I know some players feel they want to get served adventures without changing anything because otherwise they might get the impression the DM is kid-gloving encounters for them and that lessens their sense of accomplishment; I'm not saying that's nonsense, but to me the DM and the adventure writer have the same goal - creating interesting and appropriate challenges for the party - and the DM is far better placed to make that happen. And if you don't trust the DM to do right by you, well, that's a big problem right there. In the end it comes down to finding that common ground where everybody's happy with how things are done, so if you're not it's best to speak up and get a conversation going with everyone else who's involved in the game - but you shouldn't expect things to necessarily be done exactly to your liking regardless, since "common ground" usually requires some extent of compromise.