Most important property of blockchains is verifiable transparency. That is a huge deal and yes, most financial and government systems would be much better for people if they were built with that type of verifiable transparency.

Decentralization is important but isn't as important. There are many successful chains that aren't decentralized at all and are quite useful.

Most top/real projects in blockchains aren't immutable. Pretty much everything is upgradable/changeable, including blockchains themselves.

Trustless - even this part isn' true for most blockchain systems. They all contain various levels of trusting different entities.

It is the transparency and verifiability that is the key idea and most important improvement that blockchains bring.