You can't protect rights and freedoms from intrusion by the government by statute, which is kinda the whole point of having a constitution. If it's just a law saying the government can't do something, then it'll do that by first repealing that law - if all you need is a simple majority, the votes are always there.

The reason why the US constitution is so hard to amend is because of how high the bars are for the process - 2/3 in the House and in the Senate to submit amendments, and 3/4 of all state legislatures to ratify them. Or if going via state convention, then 2/3 of all state legislatures to request it, but still 3/4 to ratify anything that comes out of it.

I don't think it was a bad system originally, back before the 14th Amendment - since originally all those restrictions were on what the federal government can do, not on what the states can do. Between the states and their citizens, it was supposed to be taken care of by their respective state constitutions, which are generally much easier to amend - and even if they didn't, they wouldn't block other states from experimenting. With 14A, and the gradual incorporation of various constitutional protections on state level via it, the process to amend it needs to be more democratic IMO, and acknowledge the people, not just the states.