I don’t believe this is correct.
While the original reference (Scott Mercer) does talk strictly about ‘gaining and losing SR’, the post only speaks about SR. This is almost certainly glossing over the idea that SR is a scaled tracking of MMR, as he’s talking about the SR you gain and lose from wins and losses (which is really a gain/loss of MMR, which is then reflected in SR because SR follows MMR).
AFAIK, the only times SR is adjusted independently of MMR are for leaver penalties (which are just to make you feel bad, not to change matchmaking) and Rank Decay (which is meant to force you to grind for end-of-season rewards and not ‘rank camp’, but without changing matchmaking).
Performance-based modifiers on the other hand are meant to change matchmaking and get you ‘more quickly’ to fair matches, which wouldn’t happen if it was not a change to MMR.