I agree that the soldier needs some retweaking to fit better with PF2e if their goal really is cross compatibility, there are ways to make it work particularly if you count scatter weapons as area (I don't see why they wouldn't be as is) and allow action hero's abilities to function on scatter as well as auto-fire which would do nice things even within starfinder, some bad-ass with a shotgun making everyone keep their heads down seems cool. Otherwise there are other things they can use in PF2e, alchemical bombs come to mind along with the alchemists flamethower (which I'd count-as a weapon) be it that's going to get expensive fast if they don't take alchemist archetype.