It is true there was a pitfall with almost everyone hitching their wagon to the 800 lb gorilla-- we're seeing that pitfall now.
But we also can't deny that the only reason this is being seen as a pitfall was that hitching a wagon to the 800 lb gorilla in the first place was so darn successful. If the OGL never existed... who knows how many of these designers (either individuals or companies) would not exist right now-- with everyone needing to somehow make money only by making their own games or their own generic supplements and whatnot. The RPG design and publication scene was so much smaller prior to the OGL... because there just wasn't as much of a market for non-D&D RPGs to allow that many people to be successful (which we could define perhaps as being able to pay their bills.) The OGL and hitching to D&D allowed more people to jump in the pool-- which rose the water of that D&D pool substantially.
I think none of us would disagree that without the OGL these past 20 years and the ability to continually publish for the D&D game that the entirety of the RPG scene would be smaller right now (with every would-be designer having to go generic or not even produce at all.) I also do not doubt that due to the internet and social media that the non-D&D RPG gaming scene would be bigger right now than it is-- but with a lot less people able to make a living off of their work while within it.
So what ultimately is worse? No OGL these past 20+ years and thus a much smaller publication pool of people making money in game design (but wider in the number of games it created and served)... or with the OGL that has given people 20 years of making a living by living their dream (which they otherwise wouldn't have done?)
Yes, having the 800 lb gorilla has resulted in more people being up ship's creek without a paddle due to the potential removal of the OGL... but the only reason they are in the creek in the first place was because paddling in it was so easy and worked so well for so long.
However, I'm not sure if it was needed, and that seems to be one of the legal opinions about the OGL: i.e., mechanics can't be copyrighted.
So whose interests does the OGL actually serve? According to Ryan Dancey, the OGL served WotC's self-interest because it encouraged people to support D&D's ecosystem. Moreover, during the d20 system days of 3.X a lot of those designers couldn't pay their bills and a lot of bubbles were burst. A lot of OGL designers and publishers that made it were those that
already had connections designing for D&D or WotC. There were a lot of designers in the design scene before and after the OGL, and some of its most prominent designers were designing games that didn't use the OGL at all.
It's not like an OGL was necessary for Jonathan Tweet to design
Over the Edge, or Mark Rein-Hagen to design
Vampire the Masquerade, Greg Stafford to design
Runequest and
Pendragon, or Sandy Peterson to design
Call of Cthulhu, or Mike Pondsmith to design
Cyberpunk, or Ron Edwards to design
Sorcerer, Robin Laws to design
Gumshoe, or Shane Hensley to design
Savage Worlds, etc. IMHO, one of the biggest game changers with tabletop RPG design had less to do with the OGL and more the explosion of online fan communities. There were, for example, a lot of indie designers who cut their teeth not with the OGL but as a result of the Forge community: e.g., Vincent Baker, John Harper, Luke Crane, Paul Czerge, etc.
It seems like the primary designer beneficiaries of the OGL prior to 5e may have been the OSR community as they realized that they could reprint most materials from older editions while making minor tweaks to the pre-existing systems.