That changes nothing. The idea behind not rolling your own isn't just deliberate expert design but also open review by other unrelated experts.

> It’s a tricky thing to secure given the circumstances.

You are hand waving and you are wrong. If you are going to make claims then be specific and make solid points. The various algorithmic solutions are simple and common knowledge these days. I went into more detail in adjacent comments.

By your own logic the physical entry key isn't secure either. After all the car is just sitting around - anyone could jimmy the lock. Similarly all it takes is a decent photograph or two with a telephoto lens to reproduce your typical physical key that will get you in the door.

But all of that is entirely off topic. The broken and outdated wireless algorithm has nothing to do with the criteria used by the vehicle to decide whether or not someone is authorized to enroll or revoke a key. Tie that to possession of the physical key and problem solved. If you can't drive off with the vehicle then you can't pair a new fob either.