It’s not just a design problem
Your third paragraph doesn’t say anything in favour of on-chain vs off-chain governance.
On-chain governance is problematic because it removes node operators from the governance process, not just because today’s proposals don’t represent user interests.
I’m not saying that the processes that we have are perfect, by any means, and i love the idea of improving them. But they are (as far as I can tell) much, much better at representing user interests than anything that has been proposed so far.
I don’t think “most effective” is going to be as operative as “effective and legitimate enough to make upgrades fast enough to preserve network effects”. At the end of the day, though, it’s not self-evident that on-chain governance is much more effective than off-chain governance. Nodes installing forks is not where most of the friction comes from.
I think discouraging plutocracy and on-chain governance as an attack on the legitimacy of existing processes is all part of healthy debate with dissenting opinions. There’s nothing wrong with having incentives to replace the old with a new system, and there’s nothing wrong with having the incentive to defend the legitimacy of the existing system.