before the war all we knew was that tobirama was a powerful water-release user, and used s/t jutsu, and other techs like edo tensei
but during the war he has shown us that his hirashin, is his most commonly used used jutsu. though he said he's not as good as minato, from all we've seen, on a scale of 10, i'd give tobirama 8, and minato 9,
he's so proficient,in using hirashin.
and as for the case of kakashi, we all know how good his gotten in using kamui,..right now he should be a ble to warp himself in to that dimension and back out, without obito's help, and he can use it more times than usual, but whatever the case, is...
ftg is a jutsu that always solos kamui, because of the instantaneous release of ftg, even for someone who uses kamui, opponents like tobirama and minato would be a pain in the butt.
kamui is a s/t jutsu that tends to suck the object in, but ftg is also and s/t jutsu, but faster than kamui, so only an s/t jutsu can counter an s/t jutsu like kamui
i just gave you a write-up on their most powerful techs, i don't think their their elemental techs matter, and since they'll probably be on par when it comes to intellect, battle analysis and battle strategy and their both hokage level....i believe the only diff in their strength is kamui and ftg, and ftg soloes