^ The priority order is actually DP > DA+CnS > DA+SE, due to the massive swing in Mana that DA+CnS forces you into (cost of DA + you lose out on 1 charge of regen).

DP is your most efficient use of mana to deal damage. The difference between additional DA+SE and using DP is massive - you're seeing such "similar" results due to RNG, I can almost guarantee that.