Can you go into more details on why expertise would be more beneficial for 1v2 over 1v1? It's the same bonus and same damage going in and out so I don't quiet follow where the change occurs.
Or at least link a source that could explain it?
Mitigation & Healing. If you're not being healed then the situation being 1v2 doesn't really change anything but if you are then the " extra HP = extra damage reduction " balance is quickly annihilated. The fact that you are taking much bigger hits means that (1) the enemy team will focus you more because they like big numbers and (2) My heals on you are going to be 20% less effective than my heals on other people. I'd rather heal somebody in Recruit gear than somebody in Rakata gear because the guy in PVE gear will go down far quicker than I can heal - often even in only 1 on 1 situations. You buy 1 or 2 extra hits but pay the price of being impossible to keep up in the long term.
Now, if you are ranged DPS and can hide at the back and avoid getting focused then the situation isn't quite so bad. Similarly, if you are a tank then the larger HP will often be more useful than the increased mitigation as long as you don't mind effectively being ablative armor for a healer and dying regularly (CC and taunts are unaffected by gear.) For anyone who is going to actually be directly attacked, though, Recruit gear is better.