Well, it could be that he doesn't think most bass players want large cabs nowadays and he's mostly right. I've been prototyping a sealed 218 cab. To me it sounds insanely good and it's half the weight of some 810's, but I may not bring it to market because I have my doubts anyone would want one these days. If anything, I'll make a couple and just market them locally.
Regarding 45 degree angle ports, one small (possible) advantage is you get additional bracing along with your ports. Best I can come up with

With some of my DIY Proto cabs that use porting, I've been perfectly happy with store bought Precision ports