So has anyone done the diagonal motion, instead of the straight down? I'm guessing this is what lead to the Slant Razor?
The Slant style makes the razor cut like a guillotine, with a angled blade relative to the direction of the pass. It also torques the blade and makes it very stiff. The razor stroke pattern is identical to normal DE. A technique called a "Gillette Slide" or a J-hook allows the user to accomplish this same action at skin level, only using a regular straight bevel DE.
I've used a diagonal motion at least a few times by intuition or "default", without ever hearing of the Gillette Slide and so on.
If you can start XTG or ATG and that works for you I don't see why not. I use mostly DEs and SEs and I have to reduce in stages or the razor simply won't cut. WTG allows me to go XTG, two passes XTG in different directions allows me to go ATG. IMO the conventional progression is a good place to start and then find what works best for you.
I'm sure. But when you read any new thread about shaving and three passes, you don't hear much about it.
Probably true. But I already did this in the 1980's, so it's not like you need detailed online instructions to find it out.
My normal weekday routine is a WTG first pass. Second pass is XTG on the cheeks, chin and jawline, followed by ATG on the neck. Then a half pass(neck only) XTG. Depending on the razor/blade combo this results in either a DFS+ or a BBS. The half pass is necessary 'cause the hair on my neck grows in about 3 different directions.