The problem with being unable to change or supercede laws is the hubris to assume the laws passed are perfect for all time. We have all of human history to prove we are not the peak of civilization.
Getting bribery out of politics by removing lobbying and campaign finance is probably the best thing we can do. Having every politician run with the same amount of money and banning retired politicians from working as lobbiests or board members after office would do the most for eliminating corruption.
Even if you make laws unrepealable or changable, if the government won't enforce it then it solves nothing. We have no higher entity to complain to and get enforcement or satisfaction. And if there is some higher entity empowered and capable, we then put all trust that whatever is enforcing law can never be corrupted or coerced or have its own adjenda.