The previous failure of 4E has robbed us of a decent release schedule.
True, though maybe not in the way you think. 4e was a bid to make D&D into a higher-yielding brand. It took a lot of investment (for an RPG) and needed to generate tremendous returns (apparently, according to one insider, 2-4 times the total revenue of the entire RPG 'industry') to 'succeed' - it didn't.
5e has no such lofty goals. Very few resources are being devoted to it (notice how much is being outsourced), so it doesn't need to move a lot of product to be profitable, so it has a slow release schedule. Given how every other version of D&D eventually choked on the sheer volume of supplements put out for it, that's not a bad thing. We could finally be looking at a full 10 year run, again, this time.
Too bad 5E didn't come out in 2008 ... I doubt Pathfinder would have been able to take and hold the #1 spot in that case.
Pathfinder would have had no meaningful way to differentiate itself from D&D, in that case, yes. 5e is much closer to being an OSR game, too, and 2008 would have been much better timing, on the leading edge of the phenom, instead of jumping on the bandwagon late. Hindsight is 20/20 that way. 5e in 2008, 4e once the OSR come-back has run it's course - both with attractive OGLs - would probably have gone a lot better, and not resulted in a Pathfinder, nor the flood of OSR d20 games (3pp OSR d20 supplements, sure).
5E is wonderful but it could be so much more with just a slightly more robust release schedule. I guess I should just content myself with 5E getting published at all but I can't help seeing how much more it could be with proper support from WotC.
D&D has never handled a lot of supplements too well. Broken combos emerge, the game loses coherence, becomes too complicated, and starts shedding existing players and repelling new ones. Happened with 2e, 3e - probably would have happend with 4e if it's run had been long enough. But, it didn't happen with AD&D or the rules Cyclopedia, because they had slower releases.
Short of re-writing history, it's probably the best they can do.