A possible conclusion is that Scrum is not a robust success predictor. If that is the case, then org size will have little impact on Scrum effectiveness, because Scrum or no Scrum does not actually matter - other factors matter more.

In Nicole Forsgren's book Accelerate, she documents research that showed that a very robust predictor of effective outcomes was the style of leadership that the team had. Perhaps that is a much more important factor than whether a team uses Scrum or not.

By the way, the best teams I have ever been on did not use Scrum: https://www.linkedin.com/pulse/my-best-dev-team-experience-cliff-berg/