I am not getting it. If you don't like the theme then why don't change the theme. You can even go for custom theme options. WordPress is more versatile and has a comparatively bigger market share due to its community support.
Well. I just checked with Gtemetrix. It's perfectly fine. Sometimes, a new plugin installation creates conflict with the theme. So, next time whenever you encounter such an issue. Try to undo recent changes first.
Well, Grammarly is a very good tool. I also use it. Anyways, if you are looking to move from Grammarly then choose from the list: