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.