The contrast is here in the high amount of centralization of the code, and the relatively high amount of centralization of the proof of work (mining pools), which are the TRUE power elements in bitcoin's system; but one insists on the "decentralization of holding a copy of the sole document" in such a way that it becomes a technical burden. This is a contradiction. There's no more reason to have thousands of copies of the block chain, but only a few repositories of the code ; there's no reason to require thousands of independent verifications of the block chain by that code, but not thousands of people verifying the code itself. All this is hugely contradictory in its requirements.
If you can trust a single, centralized code depository (github) and the few signatures of the contributors ; if you know that the entire block chain is produced by just 10 mining pools with such an amount of proof of work that nobody can do anything else, but then you introduce technical limitations because of the "need" to keep thousands of copies in all basements, that doesn't make much sense to me.
I agree it's a bizarre contradiction, but I'd make the opposite argument (even though it seems to be heresy around these parts), that there should be more than one dev team and repository precisely because decentralisation is more resilient to attack. Many seem to take the stance that other dev teams
are the attack, but I suppose that's what indoctrination does to the narrow minded. Plus I'm still all for
small adjustments to the blockweight.
Also, you appear to have glossed over the part about regulatory shutdown. The fewer nodes Bitcoin has, the easier it would be for governments hostile to Bitcoin to either coordinate law-enforcement raids, or simply arrange shutting off the power, or otherwise targetting the remaining few mega-nodes to get rid of them. If everything was done in 10 big datacenters, I'd bet there are a few governments out there who would happily justify the cost of trading 10 ballistic missiles for seeing the end of the greatest tool of monetary freedom available in the world today. It's simply not worth risking.