On the subject of B/C vs, C/B, I don't think the letter grades alone give us an answer. The fielding grade doesn't give a true indication of the number of errors that might be predicted. And , the difference in the number of plus/minus plays from a B to a C OFer is so minor, it scarcely deserves mention.
I always search for bargains in pitching. I often take the key stats of a pitcher I know to be successful, and search with them as guides, setting that pitchers $/IP as the max. I hope to find pitchers with similar key stats at a lower $/IP, and frequently do. I am of the opinion that dead ball era pitchers benefit more from ++ defense than do modern pitchers, but there are some modern pitchers who do have deadball era similarities. The trade off in ++ D has to do with value. We have to score runs to win games, and good offense and ++ D is very expensive. It would take a ton of plus plays to equal the positives that '81 Raines provides, for a very reasonable price. The variance in RRF #s also is key with D- fielders. Compare 2 cookie SSs, for example, Mark McLemore and HoJo. Huge difference there.