Well...stats are useful as arguments, but just remember that 65% of all statistics are made up on the fly...
No matter the percentage or ratio of RBI, I still think its important to track the quantity of RBI. <and other stats> If a guy has 100 RBI but a lower RBI+% than a guy who has 65 RBI, I'd still prefer the slugger that hit the century mark. Just like I'd prefer a guy who has 200 hits in a season but maybe doesn't lead the league in batting average...I also don't really care who has the best HR per AB percentage...give me the slugger with 40 or 50 dingers instead.
I guess my point is that you can win arguements with percentages, but you win baseball games with the actuals.