Ah I see, sorry. You're right that they could very easily oneshot each other and that of the two Ken is better in H2H combat, but i wouldn't say that having knowledge of Ken's techniques wouldn't do anything, he could still avoid them and he does have a forcefield if that could help. Also, its not the gun that turns things into gold, its literally an aura that surrounds the Boss that turns anyone in the immediate vicinity into gold. Also don't forget the Boss can create a temporary zero-gravity field by stomping on the ground, can shrink Ken down to the size of an ant, and has a gun with infinite ammo that can spam miniature black holes and another that inflates the target from the inside when its beam comes in contact with them.
The TK extends a few hundred meters at least considering he can pluck low-flying aircrafts out of the sky with it, and considering that speed is equalized the Boss would have a pretty good chance to grab Ken and drain his life force before Ken can do anything.