Isn't developping and working on current system the same thing as trying to keep control over its development? Oo
No. You can't force anybody to run your client, therefore you are not in a position of any control. The recent developments of Bitcoin Core do not attempt to alter consensus rules.
You say it like I think it's a bad thing... I'm not putting any judgement here. Just saying that Core is dominant and they're the ones deciding how the blockchain evolve simply because they work on it and people use it. That's all I'm saying, there is no conspiracy theory or whatever.
No. Bitcoin Core does not decide anything for the network. You apparently don't understand how Bitcoin works.