I use Co-Schedule for every post. But I am also shit with titles. Since using it, I’ve gotten better, based on their criteria. I have not gone in depth with analyzing my posts as you have, but I definitely noticed that when I re-published some older articles and made the title better, it got more views.
But that could also be because I now have more followers.
It’s something to think about. I will check out the Hemmingway app as well, it seems pretty great.
I’ve never personally used Grammarly.