Originally Posted by RedsManRick
Absolutely, and that will show up in your differential. Getting 20 runs better at prevention at the cost of 20 runs of offense accomplishes nothing. But even if your offense sucks, you benefit more from improving your defense by an additional 20 runs than by improving your offense by 10. It's the change in the differential that matters, not which side you're affecting.
The point is that you can never just focus on or the other. For position players, they always both count.
This is the key distinction that gets lost in the shuffle. People that enjoy UZR use the run differential. The common reply is that you can't sacrifice too much offense, which is true. But that's never been the crux of the issue.
The point you are making, Jojo makes, I would make, etc., is that trading 20 runs scored for 20 runs prevented is a net break-even. However, while you continue to lose offense, if you could, hypothetically, trade 5 runs scored for 10 runs prevented with every player in your lineup, this is better than improving your offense by two runs over your defense.
Hence, it's the overall differential that matters, and not the dynamic of how you get there. Clearly you need some competent hitters at some point, so that's not to say a team would be advised at comprising a lineup completely of hit-less, field-more players. But sometimes there's too much an emphasis at getting a bat just to get a bat, and forget that you might be doing yourself a disservice by gaining those runs scored at the expense of runs prevented.