I don't think you can just divide in % "things that make Bitcoin Bitcoin". You are either in the Bitcoin chain or you aren't. That means, longest chain is what determines what the actual Bitcoin network is, not "what satoshi said", otherwise you wouldn't need a decentralized network, or at least he would have hard-coded an automatic blocksize increase, not leave it out open to consensus, if there is no such consensus, then it continues being Bitcoin, like it or not.
The #1 thing that gives Bitcoin value is it's certainty and safety. ANY altcoin is prime to move value from A to B, yet NO altcoin can compete with Bitcoin in terms of certainty, of a solid network that's hard to change.

Satoshi either knew that 1MB was it, or didn't realize how at some point it would be too late to make such a change and get everyone on board. If you can hop through hardfork to hardfork it just means your project it's either irrelevant or centralized. When a project gets too big, it's simply impossible to get everyone agreeing. There's no clear way to decide about blocksize increases when the project is as big as Bitcoin is.

Now what you could do is have blocks as big as possible at the beginning like BCH did, to make room for transactions, yet that posses very big theoretical centralizing risks that we may find in practice this september if the BitPico attack is serious, then it would finally be proven that big blocks don't cut it and it would be a risk to store wealth there. If miners thought that BCH was safer than BTC, they would go all in on BCH, but they know there are risks and they don't want to be paid in a token that could plummet.