In my game (2.14 opt-in, but started before the last changes, ludicrous, gifted, 300+ turns played) about 80% of the AIs (with which I have no war, the others I can't see) have nearly no Durantium, but 20% are overflowing with it (I see several 100 Durantium in the trade screen).
Thulium is used a lot by starbase modules. But I agree, balance is necessary. From most the planetary resources I have quite a lot after 300 turns, but some others are always used up, and that doesn't come alone from diferences in number of mines.
