Yes, the percentage of Twitter users that moved to Mastodon was small BUT the numbers of users was a huge increases over previous users.
Yes, many instances came up and went down BUT they had small user counts.
Finally, yes, many people tried out Mastodon but didn't stick around BUT the Average Mastodon Active Users by Month (first line chart) increased in the last period.
I'm sticking with Mastodon (and Lemmy). Besides, I know John Mastodon.