From what I remember, 2hb is specifically bad for Beastlords because of how our AAs worked, because we do not receive the same benefit from the AA as every other class that gets it, this in part because Beastlords get Beastial Frenzy AA. I noticed in your quote of how the AA works that the description in game has clearly changed. It used to have a whole "For Beastlords, this does yadda yadda yadda" descriptor that said something like double attack is not guaranteed, but on occasion additional attacks can occur with the primary hand, those additional attacks were in fact capable of triggering procs too.
Beastial Frenzy AA is double attack 100% for the secondary hand only when maxed out. Actually its like 125%. At max rank, if you equip a really slow primary like brainsucker or ofgats 1hb, you will sometimes see 3-4 hits per round from the secondary, right about the 25% mark. It's very easy to catch if you use a dagger or some other skill than whats in primary. The last and most important thing... If you barefist your primary, Melee Mastery does not work, you must have a weapon equipped. I parsed that thoroughly. Again this is all from memory, so forgive me if I am a little off, but I am absolutely certain that Melee Mastery works differently for Beastlords and that it used to have it's own descriptor for them.