Re: Is it good or bad that Core development is virtually controlled by one company?
Edit: But won't there be the threat of a contentious HF if one of them overtakes Core in nodes? Or are some implementations more benign than others?
Nope, most implementations don't break consensus rules thus there is no risk of a HF occurring even if they have greater node count (miner or not). There can be multiple implementations with slightly different features and unique wallets with no contention or risk of a fork. It does require more coordination but that is why Core is working hard on libbitcoinconsensus to insure that other implementations can prosper.
The good news is that Open Bazaar and Airbitz use libbitcoin implementations and thus are making that codebase more popular.
Nope, one and the same, still unanswered 
Yes, that why I suggested we must be talking past each other. You are better off trying to understand the code directly like I have done and read that book.