Worked out horribly badly. Almost everybody left. Only one guy liked the endless meetings during which they played council of elders and every legitimate problem was shot down with "this is not the topic of this meeting, let's have a GitHub discussion and then schedule another meeting" (you can guess how well that worked out but hint: anemic discussions, nobody agrees to next meeting day/hour and the entire thing is forgotten and then weeks later you are at fault for not pursuing it aggressively enough. Yeah...)
You should start some tough conversations, like yesterday. I deliberately chose not to engage in any position that requires a lot of diplomacy (I am 42 and been offered a PM / managerial / VP of Eng position no less than 6 times in the last 5 years) and can't advise you on what exact brand of perfumed language to use but the main message should be:
"I realize that you, X, has been instrumental in the initial company's success and everyone around appreciates that. Things did however change and our approach must change as well. Are you open to start doing things a little differently? If not, why not? Did the legal team crucify you for not providing enough written details in the past? Let's work through the initial problem and solve it, please."
...or some such.
We are people and we LOVE rituals and we love stability and we especially love when we are in a tribe of like-minded people. But this has a steep cost when a team scales beyond a certain size -- as you yourself are finding out.
At one point management has to pick between the inner core of calcified programmers, or everyone else, because it seems they don't mix that well.
Again, I can't give you an advice how exactly you should present that to the relevant people that you must raise the issue to. But from my experience I can guarantee to you that entrenched old-time developers in a company (namely those who were there when it all started) tend to become way too self-important and with illusions of grandeur. This gets in the way more and more with time.
Uncomfortable conversations at work, exactly like in intimate relationships, must be done early. Seems you're already a bit late to the party but still -- the second best time is tomorrow.
Don't delay this. Or if you find yourself unwilling to tackle the problem you better start looking for another job because culture is one of the hardest things to change in any community.