I've never even considered the lack of buff cards in most elements, because I rarely use such cards. There is Shard of Patience for anyone, though that's not very strong. Darkness has Eclipse, which I would count as a (global) buff at least in Darkness.
One possible idea for a new type of buff card would be permanents that grant permanent boosts like
= target creature gets +1/+0 or
= target creature gets +0/+2, or maybe an entropy one with
= one random creature gets +1/+1 (upped: one random creature you control).
Something like a weak creature that had 'when this creature comes into play, another target creature gets +3/+3' could also be a new idea, and help avoid the problem of card disadvantage. (it would also have fun synergy with eternity)
(don't take any of the numbers seriously, it's about the ideas rather than balancing)