I agree defensive stats are pretty doubtful.
However, that's completely unrelated to whether saving a run is more valuable, or less valuable than scoring a run. If either. It's just harder to measure defense.
If we believe Bill James old pythagorean theorem for baseball, saving a run is worth slightly more.
(Rs scored)² / (Rs scored)² + (Rs allowed)²
Take a team that scores 800 runs and gives up 800 runs. That team should be .500, according to the theorem.
Give them 900 runs scored and the same 800 runs allowed. They should win at a .558 pace.
But give them the same 800 runs scored but 700 allowed, they should win at a .566 pace.
So at least according to Bill James, saving runs is worth slightly more than scoring runs.