Anecdotally, the individuals I work with who use Grammarly are among the most proficient speakers and writers. They can write fine, but they'd prefer to spend time writing rather than editing and Grammarly picks up the slack.

In principle, I agree with you. But long ago, I worked as a copy editor, and can tell you that time in school has a weak correlation with the ability to construct a proper written sentence.

But no, nothing I've seen from Grammarly suggests that it would be much help.