Specifically, do you worry that Microsoft is going to eventually do the Microsoft thing and horribly fuck it up for everyone?
I'm not sure you are aware, but Microsoft created TypeScript.
https://devblogs.microsoft.com/typescript/announcing-typescript-1-0/
Without Microsoft, TypeScript would not exist.
I don't think there is any merit to that concern. Not only is TypeScript FLOSS, Microsoft also has an excellent track record developing high-quality programming languages and tech stacks. Take for example C#. It's been around for over two decades and if anything it's getting better by the release.
I understand the rationale behind the concern, but there is also a factor of mindlessly parroting cliches.