While signing Brown is a good insurance policy, I’m not entirely convinced signing him is the best move.
Is Brown so good that you absolutely need him? Probably not.
Signing him to an extension also means you almost have to play him because you are paying him. Playing Brown can also simultaneously delay the development of playing a younger player so the younger player can grow and learn, get reps etc.
I personally do not believe the return on investment with Brown being extended is greater than the needed reps and experience a younger player needs.
Imagine if Seattle had Baldwin when Metcalf was a rookie and Metcalf didn’t get as many snaps, would Metcalf have developed as fast as he did?
It’s not apples and oranges but I think Seattle can move on from Brown and play a rookie, game 1, and see what happens.
There’s no greater teacher than experience. Young players need reps in order to grow their talents. I’d take my chances with a young left tackle playing immediately this upcoming season over Brown.
But that’s just me.