inserted by developers who excellent at what they do have no track record as incentive designers, economic parameter setters, etc.
They do in fact have a track record. Various economic- and incentive-related decisions have been made in Bitcoin development over the past 6 years and it hasn't completely blown up yet. That includes both changes and decisions about what
not to change.
I guess this conclusion depends in part on how big a failure you think the "blocksize debate" represents. From where I sit, the blockchain is still working, transactions are being processed, etc. I don't see a major failure even in that.
I think the blocksize is the biggest
controversial economic aspect they have touched (kind of easy to change something when it's not controversial), but - see my edit - I don't think it would be good to vest power even in someone who did have a good track record on that.
I do think we will be fine whatever happens with blocksize, and are fine now, but that adoption could be set back quite a ways if too much friction is introduced and circuitous paths are taken, so I think it's worth pointing out some existing burdens on weighing on the market discovery process.