You are missing the point. Let's use kobolds as an illustration. They are, in fact, quite easy to use in a game without running any risk. Just go back to the roots, which are small fey creatures in a mine--basically a Bavarian flavor of the more general goblin. Sometimes, they morph into household fey, similar to brownies. I mixed them with redcaps, to give them a more sinister modus operandi, then made their society distinct. Like I said, easy.
Nah. I understand the point just fine. The reality is that in order to infringe on WOTC's specific interpretation of many of these things, you have to actually go out of your way to look up and reference specific things that WOTC has rights to.
For example, lets take the Kobold. Here's Warcraft's take on Kobolds:
https://wowwiki-archive.fandom.com/wiki/KoboldTL;DR Kobolds in Warcraft are kind of rat-like critters. I don't think I've ever heard anyone griping that Warcraft's take on Kobolds is inferior to Wizards' take on Kobolds. If they were missing and replaced with something else, would anyone notice? Probably not.
As you point out, it's very easy to come up with alternative takes. It's
Chris24601 that's particularly fixated on spreading FUD about creators being unable to use common tropes from fantasy & mythology in games, just because someone else started using the same word in a similar product 50 years ago.
Even if we insist on using the name "Kobold" then we could easily make monkey-like Kobolds, or bird-like Kobolds, or dog-like Kobolds, etc. Even *reptilian* Kobolds don't violate any reasonable claim unless you explicitly reference WOTC material.
Lets say in my game Kobolds are reptilian creatures derived from common lizards that have been mutated by wild magical energies in places of extreme natural or unnatural power. Just starting from a single sentence here we've immediately distinguished these creatures from whatever WOTC is selling. If we take this seed idea and use it to inform development in art/description/mechanics/characters from there, I doubt any judge would deny that this is a unique & distinct creation, even if it shares at the grossest level some similarity to WOTC's.
Coming up with this brief idea was a lot quicker for me than trying to pore through old D&D content and copying that lore directly. Plus it's way more interesting to try and come up with a fresh idea and then daydream about ways to express that in the game. Maybe my Kobolds have innate magical connection gives them some kind of resistance to magic, or some other twist. Being creative is fun. And as a hobbyist & player I _want_ creativity in material, not just a rehash of the same old, same old.
Even a lot of things that supposedly are WOTC product-identity are actually not. WOTC pretends Owlbear is a protected concept but it's actually in a ton of games, like (again):
https://wowpedia.fandom.com/wiki/Wildkin.
Good luck arguing that it's impossible for someone to come up with the concept of a chimaera creature. The FUD spreading is just really tedious, especially when it comes to stuff that could easily be created independently by a child (Bear + Owl!).