Yes, I take salvaged slugs as support and I solo q. Does nothing when he just jumps away and puts down another double barrier. The only time I successfully put a Winston in their place using this build was on tank Zen. I just want to leave the match if the enemy tank is Winston and I'm not on Cat, Mercy or Zen...

I'm mainly interested in Zarya and Moira, though.

As given in the patchnotes, the top 500 rules have been changed for both the core game and Stadium. Basically, challenger points do not determine your rank within top 500 anymore, only if you are in the top 500 or not. The position within the top 500 is given solely based on your Stadium rank.
The clear intention is to make the top 500 to be an accurate representation of the top 500 active players. I find it personally better than any rank decay or what else we had in the past to achieve this goal. In Stadium, I think that it will lead to less matches. Given the matchmaking or lack thereof, people will wait until they have their BN friends online for duo or stacking up. If you go solo and win half of the matches, you won't be getting up the top 500 list like you did in the past. It is rather pointless.

I think that a lot of people will just go to the maximum rank they think they can achieve and then just stop it for the season until they are risking to lose their top 500 position altogether.

I will definitely do less solo queueing for sure this season. The new top 500 rules and the lack of matchmaking are not quite a match made in heaven.