I understand your point. But I think there is one aspect that you might be overlooking. Now this is with hindsight, but lets just say Paizo would have gone with 4E at first. And then, when the deition war storm broke loose, they would have realized that there are a lot of people who just do not like 4E because of the design, which these people think sucks big time.
This is a target group that WotC did not reach anymore and taht would have been looking for somebody to pick up the 3rd edition stick and march on with it. And I am 100% sure that Paizo would have done that. It is just too big of an opportunity, too many business chances there.
If Paizo they had become heavily invested in 4E via a 4E OGL, then they would be less likely to suddenly change tack. If the the OGL 4E market share was declining sharply and people were clamouring for 3E support, then sure, they might start to slowly change course doing a few OGL things at first and then more if those were successful.
However, if a lot of people strongly dislike 4E mainly because of the design, then they aren't going to keep playing it, period. It doesn't matter if the OGL is around or not. Why play a game you don't enjoy? If the game isn't enjoyable to your customers, then you have much bigger problems than a game industry rival that you helped to create.
What a 4E OGL would have done is give 4E players more options beyond those WotC comes up with : new settings, adventures, alternate classes, powers with a niche theme, etc. This might have helped keep players who were bored with what Wizard's putting out and perhaps drawn new players in because it's a bigger ecosystem appealing to a wider range of gamer tastes.
As I posted above, in my opinion this could have been avoided with some sort of other legal agreement. Something that gives the right to use the rules to a company but retains the rights to stop that usage with WotC. Combine this with a lower fee than the 5000$ (was that the OGL fee, I do not remember) and I gues WotC would have been good to go.
I would say, same effect as the OGL, no loss of IP.
I believe the $5000 number you are referring to is tied to 4E. There is no fee to use the OGL. If they had used a more restrictive expiring license, you would not have had that vibrant d20/OGL ecosystem and D&D would have been the poorer for it.
I do not think they were doing well, because they build up competing products within the company that people could buy. But the fact that they were able to create all these worlds shows that you had a lot of design potential which could have been used to satisfy by far the most DnD players.
Yes, even though it may have contributed to TSR's demise, I loved all those 2E settings. To me, that was the D&D Golden Age.