Not really. You can describe a monster however you want. You could describe a Mind Flayer as a hideous insectoid creature with a jagged chitinous barb that punctures the head and sucks out brains. Really, D&D could just have a 4-8 generic statblocks that work for all monsters and just lists of unique powers that you can mix-and-match to create whatever you want. The Monster Manual could be 32-pages long and cover everything with that method.
Fluff defines a monster.
Again, mostly disagree. While the twist would throw some people off, the majority of players I’ve had in my game concern themselves first with the danger and mode of attack of monsters, then the motivations of the monsters. As long as it is still a threat of instant kill by brain removal, little of importance has changed. Same thing with other iconic foes like a rust monster; as long as that ability to destroy gear is present it’ll inspire the same fear regardless of how the creature was formed or what it looks like.
I know this makes it seem like I don’t care at all about fluff, and that’s not the case, but to me mechanics will always be of vastly greater importance.
OMG, what if they released an actual MM2 and there were only 50 good ones?! Or NO good ones!!
I don't think that's likely though. When you're doing 100 monsters you have time to make them all count. When you have 300, you're going to slack off with a few. Picking the best 100 monsters for Volo should make it easy to really have some great foes.
It’s not just about being good, although that is a concern, but about being
new. If Volos retreads over a bunch of variations of creatures already in the MM1, that’s less attractive to me unless they really knock my socks off as far as playability goes. The new fire giant gives me hope that this is the case, but I’m still hoping we get more diversity, which is less likely the fewer creatures you have.
Except you can enjoy the Volo's Guide when not actually playing just by reading the entries. And the fluff might give you ideas for adventures or suggest how to use adventures. And it will be a book that is usable for longer, since fluff doesn't expire during an edition change.
Plus there are races. So it will have that impact.
The races thing will be useful for some tables, but not mine, and as someone who is primarily a DM that only lessens the value for me, since now 20~ pages are devoted to content that is largely useless to me.
As for the lore, lore is easy to come by. There’s no shortage of prior D&D lore to draw on, a huge bevvy of fantasy literature, real world mythology, and of course video games and movies. Reading a short list of 6 potential bonds for giants, that are all fairly stock as is, isn’t super enjoyable nor terribly helpful. I don’t begrudge people who do like that content, I’m just saying it makes the product less attractive to me personally.
Also, with the DMsGuild and OGL, I don't see as much need for another "big book of monsters". Any monster you could want has probably been updated a couple times. And with stuff like the Tome of Beasts out there we don't *need* new monsters.
I’m not really sold on either of those, to be honest. OGL is probably the best bet, but it’s hit and miss and outside of some big providers is mostly limited to digital and kickstarter releases. Not exactly a dealbreaker, but it’s nice to have a physical product made by people who presumably have the knowledge and resources to design and playtest them effectively.
Also, please don’t trot out the ‘need’ argument. ‘Need’ basically never applies in relation to D&D, people don’t ‘need’ more feats, classes, items, monsters, traps… so on and so forth. But they want them, and at least some want them from official or at least professional channels.