rilfes are not the best at long range,
their best preformance is close to mid range. They dont have sandbags stock. They either need to close in or avoid the engagement. They have a harder time defending a position because of these. And before you start i am not saying rifle are up. The maps are to open for them to shine.
They do not have a harder time to defend positions because Ostheer are bad at attacking.
Try attacking with grenadiers from out of cover vs riflemen in cover and see what happens.
But that is besides the point riflemen are much more flexible when it comes to fighting having decent DPS at all ranges and thus it is not "the enemy dictates the fight in by far most cases"
releying on a mortar to bleed is quite a bit unreliable. As usf you get rifles (midrange)rear echelons and a mortar and ambu at t0. Other factions get mg's scout cars/transport, at gun, long range and cqc inf or sprint. So using doctrines as usf and pathfinders in paticular to fill gaps so early on makes sense imo. Neither paths or scott imo are op.
USF mortar is in line with other mortars and it will bleed the enemy unless he can fire back.
Ambu comes early but not so early, its also the most vunerable imo esp if used as forward healing.
Also if what your implying is true about mortar and ambu why is usf usualy more mp starved then most faction when not using paths? They cant seem to float mp such as okw for example.
Destroying a ambulance in a 3vs3 or 4vs4 in the early game is not easy at all.
OKW float mp only when/if they are starving for fuel (and even then mostly because they can not build cashes like other factions).