here's the basics:

150 + 190 + 250 = 590 (SP combo)
150 + 190 + 270 = 610 (SE combo)
150 + 200 + 280 = 630 (BB combo)

maim should never drop off, so we can ignore that as its effect is consistent across every combo

SP -> SE:
SE debuff (+10%) is up full time, so:
(590 + 610) * 1.1 = 1320 potency for 6 actions
1320/6 = 220 average potency per action

SP>SE>BB:
SE debuff will only be active for the SP and BB combos, so:
590 * 1.1 + 610 + 630 * 1.1 = 1952 potency for 9 actions
1952/9 = 216.9 average potency per action

SP>BB:
SE debuff is never active, so:
590+630 = 1220 potency for 6 actions
1220/6 = 203.3 average potency per action

SP>BB>BB:
no SE
590+630+630 = 1850 potency for 9 actions
1850/9 = 205.6 average potency per action

so:
SP>SE is the winner because you have 100% up time on SE


2.

SE>BB is going to be your highest dps combo because it's the only one with 100% up time on the SE debuff