That is verifiably false. Blizzard recently removed performance based mmr adjustment, which you can read about in this blog post: Overwatch 2 Developer Blog: Explaining matchmaker goals and plans, part 2 - News - Overwatch.
Q: So you don’t take the number of eliminations, damage dealt, healing provided, or any other scoreboard stats to adjust my MMR after each match?
A: In Overwatch 2, your MMR adjustment after every match is not impacted by your performance in each match (regardless of your skill tier). This is for a few reasons. We don’t want players to be focused on doing things other than trying to focus on the objectives and win the match. Dealing the most damage or getting kills won’t help your team if your actions don’t help them push the payload or capture a control point. Also, for some heroes, especially those in the support role, it can be challenging to determine if the numbers they produce reflect their skill.
As for the bugs regarding the inaccurate rank adjustment, those are very much still in the game and there are numerous threads about people experiencing those bugs posted daily since Overwatch 2 launched, which if you’d like you can read more about in the megathread: The Competitive Bugs Megathread.