Who said bitcoin is on its maximum development? It's still being developing all time and there are a lot of space to grow for developing.
Can we still expect better coin than Bitcoin?
If we think about different features of bitcoin with some other existing coin, they are better. You can get a better coin but you can not get
the most decentralized coin.
Yes, I forgot to mention decentralization. When it comes to decentralization, Bitcoin is the best among the rest. Unlike other altcoins which have owners and CEOs and presidents and development teams who are personally identified, Bitcoin does not have any. Bitcoin has only Satoshi Nakamoto. And Satoshi is not a person. It is just a name. What's in a name? Nothing physical. It is an idea.