DMs who say KotB sucks because it doesn't have everything fleshed out are sucky DMs.
Well, first of all, most of us here saying that it sucks have much more complex reasons than "because it doesn't have everything fleshed out". For one thing, that's a nonsense complaint - no adventure or rules set has everything fleshed out - not even the longest, most linear, most detailed adventure path has everything remotely fleshed out. Every adventure requires preparation work because no adventure is remotely complete. Every adventure requires adaptation, both to suit the tastes of the GM and to suit the tastes of the players. It's just normal for an adventure to require fleshing out.
Secondly, do you really have any thing to add to this conversation other than to insult people?
And thirdly, sans doing something like 'Critical Role, it's impossible for me to demonstrate my skill as a DM over the internet. But what I can do is demonstrate my skill at fleshing things out and content creation, which I consider one of the key skills that would demonstrate quality in a DM, precisely because everything needs to be fleshed out.
For example:
http://www.enworld.org/forum/showth...ing-A-Bestairy-of-the-Sometime-Lords-of-Chaos
http://www.enworld.org/forum/showthread.php?310345-Queen-of-the-Demonweb-Pits-what-s-so-bad
http://www.enworld.org/forum/showth...-the-nobles-of-an-imperial-capital-in-decline
http://www.enworld.org/forum/showthread.php?334623-ToEE-Help-me-flesh-out-the-elemental-caverns!
http://www.enworld.org/forum/showthread.php?509229-What-do-the-PCs-find-in-a-City-of-the-Jann (read a bit into the thread after I figure out what the OP is after/needs)
And that's just a sample. So yeah, fleshing out stuff is something I can do.
The thing about something like 'Demonweb Pits' or 'Temple of Elemental Evil', is that even though those are terrible modules, they are terrific ideas for modules. They have good solid bones, even if the fleshing out that the writer actually did is at best uninspired and at worst pedestrian. The thing about B2 is that it's not even particular good idea for a module. The flesh in some parts is actually pretty decent. Gygax writes tons of interesting details into individual encounters of the module. But the underlying structure and idea of the module isn't that great. So what you actually find in people that are using the module is that they are taking just the skin of the module, and rebuilding pretty much everything else. I mean, even among the modules defenders, a lot of what they seem to be using the most is simply the 4 pages of the module that sketch out the "Keep" environment, and just stock piling the keep with what they need. Or you'll hear of people who build a vast sandbox around the module, detailing empires and villages and so forth filled with other opportunities for adventure, and creating back and fore story that B2 doesn't have anywhere, and then they have a great campaign which involves a ton of other stuff that has very little to do with B2, and more to do with the fact that their characters were also playing a bunch of custom content and modules like "B1: In Search of the Unknown", "L1: The Secret of Bone Hill", "L2: The Assassin's Knot" at the same time and often instead of playing B2. So yes, when you do that and you do it well, you'll likely have a fun time. But using that as evidence that B2 is a great module is a lot like using the evidence that I was able to give a sketch for fleshing out Q1 as evidence that Q1 is a great module, or that groups played GDQ with a skilled DM and enjoyed it.
But I can hardly think of a module less worthy of investing all that time fleshing it out than B2.