Why are my Platinum+ games lower quality than my Gold+ games were?

In 9/10 of these games, one team is 3-0 or 5-0 by 5 minutes, and has won by 20, if not sooner.

After going from Gold III to Platinum III with 63% win rate Udyr, I can't no longer stand to jungle at this rating.

The majority of my losses have two of my lanes constantly dying without the enemy jungle doing anything, which forces me to choose who I want to leave to feed or whether I want to deal with one really fed champion later or two kind of fed champions, because I can't be in two lanes at the same time; these games are hopeless. Or in some cases, I don't have a choice, because one of the lanes is so fed that I'll just die attempting to gank it.

The same applies for my wins: I often don't even have to do anything, because all of my lanes are stomping the opponent so hard, and they can 2v3/1v2 if the enemy jungle even tries to gank them.

This is a ridiculous situation that really needs to be improved, whether the issue is that Platinum+ has a massive skill gap, or if it's just that feast/famine champions are poorly balanced.