SR abuse will always be a thing though.
During dive meta mediocre D.va and Winston mains were able to climb hundreds of SR. I had a friend who was a 2800 Genji main or something but then when dive meta came around he played Winston in a 4 stack and got to masters in like 4 weeks. I myself was able to climb like ~400 total sr as D.va even though I’m not great as her, you just follow your Winston and spam matrix right?
During the Junkrat meta Junkrat mains were also able to climb lots of sr with not much ‘real mechanical skill’. Now that Junkrat isn’t very meta its left many Junkrat one tricks in tiers way above what they should be if they were to play other heroes, struggling to win, I have several people on my friends list in this situation.
During season 10 before Brigitte was fine tuned Brig one tricks were able to climb hundreds of SR, which was helped by the brawlier meta at the time (Rein, Zarya, Hanzo).
SR ‘abuse’ will always be a thing, it’s not just a Mercy specific phenomenon. Mercy was just like this for longer. The problem Mercy mains have now is not that they can’t one trick her to masters and gain crazy amounts of SR, it’s that they can barely maintain their SR with her. I’m not exactly for one tricking, but you should in theory be able to at least maintain your SR with one hero, even if you can’t climb.