Have you ever gotten perks on other *A carriers that are not published benefits? Perhaps UA shouldn't be giving E+ away in advance, but if there are open E+ seats shortly before boarding, I don't really see a problem with giving them to other *Gs.
LAX
I do, and I guess that's why opinions are to each his/her own. a) most other * carriers don't have the ability to do so much for so many, so the "it all equals out" doesn't really work out that way, b) the cost is carried by UA with the reduced capacity, not OA, so the rewards (sales of E+) should be given to UA, c) plenty of OA elites pay to use E+. d) it lessens the motivation to shift the flying to UA, when they can get the benefits by flying the other carrier and on the occasional UA flight, they get the benefits as if they were UA loyalists (decreases future bookings on UA as carrier of choice.)