This is only my opinion and please allow me to share it with here.

In my opinion, it cannot be modified or repaired because bitcoins have their own decentralized order for its transactions. Because of this, every bitcoin transaction has its own transaction fee and it depends on the bitcoin sender, they had different rates, especially when it is used for paying bills and receiving and sending bitcoin to fellow bitcoin users in different kind of wallet addresses.

And immutability is the definition of irrevocable, therefore any price and rate regarding bitcoin transactions cannot change. And while the basis of the minimum fee for transactions made by bitcoin cannot really change because bitcoin has its own time frame in every transaction it makes.  That's all.