How come should there be a power to grab in an open source project? Writing code is power? If no one use their code, programmers have no power over anyone. It is the crowd thinking that they must use so called "core" software give programmers power. But core is not a registered company, neither a trade mark, anyone can call themselves core.
It is possible. You get to control the main implementation (currently Core); i.e. you try to make your own implementation the main one. There are only a handful of people who have Bitcoin Core commit keys right now.
Architecture wise, any bitcoin software can be called a "core" software: Blockstream core, unlimited core, classic core, XT core etc... because their architecture is the same.
As soon as you start writing nonsense such as "Blockstream core" you easily reveal just how biased and deluded your viewpoint is.
However I don't see how segwit can be called "core" since it is totally another architecture
This makes zero sense.
Keep in mind that you will get no unbiased opinions here. Every single poster here gave you a suggestion based on their goals.
Not necessarily, but yes.