When WotC proposed the original version of the OGL that started the uproar three years ago, did it actively threaten the ability of ENWorld Publishing, Draw Steel, Kobold Press, Darrington Press, Arcane Library and the like to publish their games?
I can't speak for the publishers, and would be interested to hear specific perspectives, but as a general principle, yes it did threaten publishers.
There were several different vectors of harm.
First off, WotC was trying to push the idea that they could deauthorize the existing OGL, I think 1.0a. Now, legally, the consensus from people who weighed in (including actual lawyers) was that WotC probably couldn't do that, because the OGL was explicitly designed to prevent that, but that they could cause significant legal problems for publishers that might dissuade them from using it. WotC was particularly keen on this seemingly legally nonsensical idea that no new products could use the OGL 1.0a, and existing products couldn't be updated.
So that by itself was basically an existential threat.
Second off, even if you agreed to OGL 1.1/2.0, there were a lot of extremely threatening and problematic provisions being suggested by WotC. Two of them were:
1) WotC will take a cut of your revenue (not profits, revenue, so could easily turn profit into loss) if your revenue was above a certain amount. Most smaller/solo publishers would have been safe, but a significant number of publishers (including many of the ones you name) would have been caught by this, and as well as just the money going, it complicated running a company quite significantly, and opened you up to potential legal disputes with WotC as to whether they were getting what they were owed. And they wanted this for basically nothing in return. The only "consideration" offered in this contract was "We let you keep using our licence", which yeah not really mate.
2) WotC can cut you off at any second for any reason. They were very clear on this, offering a paranoid vision that some Nazis might make a D&D product and it would be terrible for them (guess what, WotC, that already happened, nobody cared - and there are tons of weird and bigot-y D&D 3PP guys out there, and just they sell what they sell to who they sell, and the papers aren't like "D&D is for Nazis now!!!"), so they had to have the ability to instantly de-authorize you and stop you making/selling any new OGL products, oh and importantly, you had to send all your stuff to WotC to REVIEW BEFORE PUBLISHING, which like hell no. Even if they weren't going to rip it off, that's a huge extra delay and anyone whose task is to find fault, is going to find fault. Presumably if they did find fault, you'd have to go back and forth with them until they were happy. This is not something existing publishers were typically equipped to handle (certainly not those who didn't work with licenced products), and it means that like, if say, anti-trans views in the US hardened, WotC might decide your trans-friendly D&D product was not acceptable and cut you off (that's just an example, of course, not something I regard as likely).
There was a lot more bad stuff too but even just that was all existential.