As subject goes, is Bitcoin the maximum version?
Is it still possible to develop it?
or
Can we still expect better coin than Bitcoin?
Obviously not. Every technology does need a development otherwise it will be degenerated. There's no such perferct system or technology ever created because if there is then we don't need to invent things that is way more efficient. Bitcoin may seems efficient but it does need an improvement in terms of
security, speed and more. I believe that Bitcoin is in development stage and it will always be.
as you mentioned, bitcoin still has a problem that needs to be refined, and it's not easy and has to go through consensus several times. No other coin has the same level and most of the popular altcoins have really become centralized and cannot be compared, other coins will remain alternatives that actively support bitcoin.