Rocketeer

I've actually been wondering and thinking a lot about the theory behind Slant Shanks recently myself. I grew up with my mom's Golden Touch & Sew, bought my first machine and several others that are straight needle machines, and ultimately fell in love with and restored a Rocketeer. My next project is the straight-needled 319.
It seems to me from the reading I've done that the majority, if not all, of the reasoning behind the slant shank is to put the business end of the machine closer to the sewer and make things more visible. When you think about what slanting the needle actually does for *sewing* though, it's definitely true that that slant effectively increases the relative thickness of the material being sewn. Straight through a thickness of leather is the shortest distance from one side to the other; slant the needle and you're lengthening the path, even by a little bit. So I wonder if the potential problems of slant shank ultimately could outweigh the "I can see the work better" factor, particularly for certain things like sewing thick material.
I have to wonder if for thick/tough material, a straight needle machine like the 201 or others (or if zig zag is needed, a 319, 237, etc) wouldn't be a better deal. Also, I bet industry never used slant-shank machines for precisely this reason...

(Along the same lines.. the zig-zag feature of machines like the 401, 500, etc is "swing needle" and the needle literally swings left and right, which also means a bit of an angle through material -- but the 237 sees not only a straight needle bar, but the entire bar is moved left and right for zig zagging, which means at all times and on any stitch, the needle is going straight through the material.)

Just some thoughts!
Matt