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.
This is why people create alternative coins, they want create something that blockchain doesn't have, but I agree with you there are so many altcoins out there which better than bitcoin but one thing that those coins don't have, yup the decentralized nature.
Yes, both of bitcoin and blockchain still developing and has so many potentials that can be expanded more by the community, you might check the project on the GitHub.