USF was generally doing that prior to the the mortar being used and they still can do it. 4 rifles into Captain or now 3 Rifles and a mortar into Captain. Grenades themselves are more of a mid-game upgrade when things are settled and you're now in the process of beefing up the Riflemen.
I don't get how adjusting the mortar will make it useless if we were to take the CE mod mortar for example. It can still block off garrisons with smoke and provide some damage against infantry, but doesn't do enough to force weapon teams to retreat by itself, is prone to getting counter-bombed, but does has the ability to keep up with aggressive riflemen. It also won't overlap with the Pack Howie.
Furthermore, giving it less range, means its easier to attack the mortar itself and harder to hit units that are operating in the back aka MGs. You probably won't kill it, but it's much easier to force off and means the USF can't simply keep it back without micro.
I'll say it again, USF needed a mortar, but they did not need an 81mm.
Also, if you're complaining about the Stuart as well, make a topic for that and how USF can generally rush out their light tank the fastest and how it can lockdown the majority of the lights/outright kill them with the push of a button.
Imho, Riflemen early-mid game, even with a mortar aren't an issue. The issue is how fast the USF can pump out their light tanks to bring that shock value forward when faction such as Ostheer might be just getting their first Pak out or their own LV without much room to grab AI units like PGs due to the need to counter light armour and no real method to force the USF to react outside of pissing them off with snipers. OKW, at least during a period of time, can start to heavily pressure USF and they'll have things like StGs coming online along with grenades which Rifles can't deal with unless upgraded or doing it from the start with the Sturm + Kubel push.
mortar is a force multiplier. 4 rifles + 1 mortar is better than 5 rifles. There are some stuff that rifleman just can't do, namely acting as artillery and removing machine gun from a safe distance with either explosive or smoke.
the mere existence of a t0 mortar make the USF that much more deadly and make it more diffcult for the wehr to survive that harrowing early game. Not only does the wehr have to worry about rifleman, they now also have to worry about a mortar.
And
USF doesn't need a mortar to survive the early game. They have always held the early game advantage with their rifleman and superior light vehicle. If the USF lose, it's usually because they let the game lapse into mid-late game where the axis traditionally dominate.
the only discernible effect of a t0 mortar unit is to strengthen the USF's early game dominance and provide the USF with less incentive to buy the grenade upgrade.
Remember that the USF's primary smoke dispenser was the grenade upgrade. A mortar basically eliminate the need to buy the grenade upgrade in the early game. You also don't have to worry about munition early on as well. The most abundant resources in the early game is your manpower, and a mortar just capitalize that fact.
and the 60mm mortar feels like it's trying to be both crappy and useful at once. I don't see the 60mm mortar being that useful into the late game. It's a niche unit solely meant to boost the USF's early game where they honestly don't need the help. It's trying to boost "diversity" at the cost of balance.
the availability of an early mortar tube only exacerbated the ease at which the USF buy their stuart. Without the need to buy the grenade upgrade early on, the USF can rush Stuart that much faster.
Trying to dismiss the effect of an early mortar unit on the USF teching speed is missing the larger picture. Unless some drastic changes is made to the stuart or the ost, I don't see a t0 mortar fitting into the USF.