Regarding the first point, men on base ahead of someone HAVE to influence stolen base totals. If there is a man on first base 10% more often than was previous, when Ells gets on he'll be 10% (not factoring in doubles, etc) less likely to steal second. When your leadoff guy is batting after the guys who dont do much damage, he has clean basepaths to run. Thats not the case in the 7 spot. Hard to steal a base from first when Big Papi is on 2nd
Regarding the second point, yeah I am talking about a situation where Green is knocking in Bay or Drew instead of Ellsbury. They aren't being erased, I agree, but what i am saying is, why would it matter if you have guys at the bottom of the order who cant knock in guys often from first since the guys who would be batting instead of Ells in that low spot would be an XBH hitter anyway.