The problem with mills is that it fixes the only "weakness" tommies. Tommies will beat most enemy infatry in range and thus if they want to win the engagement they need to close where mills helps them.
this can be true that mills bombs used to have no minimum range, but it is fixed. And close range is not the only weakness of tommy since they dont have a snare.
As for USF comparison it does is not that accurate due to faction design. The important differences here are that, USF grenade is an more of an offensive tool for USF while mills for UKF is more of defensive tool, USF are more pressed for fuel/munition for getting heal/hmg/light vehicles than UFK so it harder for them to afford grenades
the design is nowhere near the best, but mills bombs is deffinitely an offensive tool, since it is the stock garrison clearing option out side of wasp (not counting base arty). event if tommy is a long range oriented unit, using mills bombs to have to self-defense again close range unit is not a bad thing i belive since it require a certain lv of skill to use and wont guaranty wining the fight since it can be doge and will become easier to doge with the new impact delay.
i will say it is fair if one can have a chance to flip the engaement or at least inflict some damage before forced to retreat when a close range squad charge right in to his section. And it is needed so that other players have to think twice before commit the charge instead of auto close in one see a section..