I climbed S2 to GM3 by filling every match. Only didn't fill in two.
My climb was smooth with a ~60% win rate. This changed at D1/GM3, where my win rate tanked to 52%, and I had to pump out 20 games around D1 alone. I chalk this up to a few things.

1. I started playing more in the afternoon, instead of morning/midday. Meaning I stopped playing with NEETs and started playing with teenagers. The NEETs were noticeably better, unsurprisingly. Better at playing as a team, played more aggressively, and understood the importance of spacing and momentum. The teenagers were mostly shit. Weak mentals, lacking knowledge of counters, and played very passively. Most fights boiling down to who got ult first.
2. There are too many people in D1/GM3 who suck. I remember in S0/1, people would swap team comps, change roles, communicate, etc. Diamond separated the wheat and the chaff. But in D1 today, I had WAY too many games of stereotypical QP shit like 0-5 Duelists refusing to switch. I even had one match where our Thing was emote spamming with their BP, despite it being ranked.
3. I started getting burnt out and played a lot worse right around D2/D1 and was not contributing very much in some games.

My hours were, surprisingly;
6.5 on Vanguard
4.9 on Strategist
4.5 on Duelist

I can say without a doubt, that most games boiled down to good Vanguards. The vast majority of Duelists were not good enough to get consistent picks on their own, and relied on their Ults to make plays. Except, they would often get countered/outplayed and completely waste their ults. However, I CONSTANTLY witnessed team wipes from Agamotto, or Magnetos nuking Supports, or Hulks busting up teams.
HOWEVER, whenever there was a good Duelist, (like 1/10 games) they hard carried.
Strategists just had to fill a basic competency level, and only like ~50% of them actually could fulfill that.

Overall it was fine.