I haven't had enough time to analyse the situation as deeply as you clearly have what with work, my own projects and my degree work, so all I can say is that my experiences don't mirror yours.

If your only argument is bloaty, badly written HTML etc. then I really don't think that is a sufficient no-no to avoid vBulletin. When I revisit the forum homepage at vbulletin.com, I get hit with a 20k download (at 56Kbps thats about 3 seconds, so if your 22Mbps connection is taking 30 seconds to load that, then there is something seriously wrong with your connection, your ISP has really bad peering arrangements, or you're on some seriously high contention service... regardless, on my 8Mbps service the page loads in under 4 seconds and a large portion of that is courtesy of facebook and google). It's never going to be as neat and tidy as hand optimised HTML granted, but if it's the choice between vBulletin with all the features we want to provide in one easy to maintain platform and some open source product which requires a bunch of plugins/modules to do what we want and so becomes a nightmare to maintain, then I would go for vBulletin EVERY time.

Some people don't like vBulletin... I wasn't keen until I used it and ran a site on it. In my experience, it just runs. In 8 years of running a vB board, I have NEVER experienced any problems like we have experienced here from time to time (and we've used SMF and phpBB). From an admins perspective, thats a very appealing direction to go in.