On the other side of this debate, engie, a return of "60-80%" of the "distance lost" does not necessarily correlate to a similar increase in offensive production. For instance, if the "20 extra feet it adds to a batted ball" is 20' on the end of a 350' hit, that's just a 7% increase in distance. I apologize in advance if I'm misunderstanding you, but it perhaps bears emphasizing the % increase expected is only of the, "% lost from the switch to BBCOR" not to be applied to, "overall offensive numbers".
If all they are telling us us that the new balls give us 15-20 more feet on a batted ball, it is just speculation on what % impact that will truly have on overall offensive output. The best we can probably do is look at numbers from the pre-BBCOR days, and guess that the offensive production might be close to what is was then. Still a guess, but an educated guess.
So, how much has offensive production gone down since the switch? Are there any other significant contributing factors, such as adjustment to pitching mounds, quality of players, particularly pitchers electing to play college ball, etc?