Yeah, thats what I am describing is that we basically have to rely on 3rd party libs when JS has some but not consistent support. The goal of this is to have builtin methods to check. These suggested methods are an extension on what JS already has implemented.
The istypes proposal looks interesting, however It seems to be inactive since 2018.
The proposal also could be extended for other classes like inspect-js does (example: RegExp.isRegExp()) and still be consistent.