Surprisingly, this actually really works! The only problem is I find it's really tedious reading my book backwards BECAUSE I'm not getting into the story at all. So, I've actually only edited a few pages that way, usually my opening pages because they're so important. But you catch everything this way.
Like you, I save all the grammar, proofing, and spellchecking to the end. From your post, I'm guessing most of the grammar issues you run into in your writing are just mistakes, like typos and such. Because you clearly don't struggle with grammar!
I find a lot of errors occur when I make changes. Maybe I'll take out only half of a sentence or accidentally leave in a stray preposition.
I miss a lot of this stuff when I'm rereading, because I'm already so familiar with the words I end up skipping over lots of them--and sometimes skipping over the words that shouldn't be there.
This is where family and loved ones really come in handy! While they love you way too much to ever criticize your story (that's what the beta readers are for), they're great at catching typos, accidental spaces before periods, and pronoun disagreement.