Even if you're a "10x engineer" the ability to describe how you would fix or replace things using just small changes is extremely valuable. And the inability to

Even if you're a "10x engineer" the ability to describe how you would fix or replace things using just small changes is extremely valuable. And the inability to put together a moderately-detailed plan for that is a big smell. If you don't actually understand the full set of changes that will be required in order to get to your desired new end state, how can you evaluate whether "just write the whole thing" is a one month, six month, or longer project? There are going to be nasty edge cases and forgotten requirements buried in that old code, and if you discover them for the first time halfway into your big rewrite... you might suddenly find you're only 10% into your big rewrite. (Especially if you're a "10x engineer" you should understand what makes big rewrites hard and often fail or go way over schedule/budget. You should've seen it all before.)