Up front – I have a 650b which was bought because of the bike not the wheel size, it was nearly a deal breaker because I was worried it may die out in a few years and I couldn’t get parts – decided the bike was worth the risk.
I’m glad I did as it is very good, now if I had the choice between the two (exc 29) I would stick with 650b because it does feel better for me. I’m not really a cynical chap but of course, if they find something that is marginally faster (even if only by 0.00001%) then it will be promoted and companies will go for it. Of all the new improvements on my new bike over the old one (08 spesh enduro to cube stereo) the best thing is the weight saving of all the carbon, next best is the better suspension (not hard), after that I would say it’s probably the wheel size. The tapered head tube isn’t a big notice (caveat: the E150 forks were ridiculously stiff) but the least noticeable is the X12 rear axle but that’s being snapped up around the place.
I’m afraid it’s the world we live in, road bikes have less to improve because the terrain is much more uniform – though look at debates over sportives & now disc brakes. It’s not just MTBing.
It’s not the new Betamax because it is slightly faster and therefore the big bike companies will go for it as that is more their goal, once they go for it the others have to follow suit.
Please note I say faster not ‘better’ or ‘more fun’, that is in the eye of the beholder. So smaller companies may prefer nimble & agile over outright rolling speed & therefore will feel bullied into it. I think that’s your issue – the pursuit of speed as everyone’s goal on their MTB.
Now on a personal note, I like speed on an XC route and a DH route but I also like jumping & big drops so 650b fits very nicely for me as a balance. I wouldn’t go 29er as my only bike because I like doing dodgy landings off big drops but if I could afford two I would have a big DH bike in currently 26 but either that or 650 would be fine & then a 29er for XC.
What I really dislike is the self righteous attitude that argues anything other than 26 is rubbish, chill out man and look at the positives of all the differences from 20” up to 29″, innovation is very cool!