Switching isn't rewarded at all, I play in a six-stack with discord friends (we are all bronze/silver/low gold) and we are climbing together.
One match I switched ONCE, just to defend better as Symmetra while the rest of my friends didn't because that was the only change we needed to win.
Despite having all golds (silver healing tho, because I played Ana first round) I gained 20 SR while the rest of them gained 30.
For a game that encourages players to switch midway in game, it doesn't reward players who do so at all.