The question is irrelevant because OP's not about grammar accuracy or comprehensibility but about domain expertise. Grammarly has no idea what you're talking about, only how. It tries to get around this with the web-scraper activity mentioned elsewhere in comments but obviously that's a bad way to do it for many reasons.
> An algorithm is isn't going to be able to clear up miscommunication more accurately than the person who receives the message.
The whole point isn’t accuracy. Grammarly improves the clarity and accuracy of the message so another person doesn’t have to. The recipient can focus on the message, not applying their superior ability to clear up miscommunications.
So, I tend to agree with you. Whether or not this person has tested Grammarly is somewhat irrelevant because they clearly don’t understand why it exists.
Yeah, I'm looking at this and perhaps it's useful to distinguish absolutely useless from of limited use.
My guess is -- the improvement one might get from using Grammarly might be equivalent to "a faster version of, let me read a BUNCH of examples of similar writings to spark an idea of a better way to say a thing?"
In other words, it feels like the thing that Grammarly might be useful for probably lean "syntactical" over "meaningful?" Something like that.
