BelgianRattlesnake
Remember we are talking about low fire-rate guns in class and this time you take the MP40/STEN as an example for the second slowest rate of fire for the SMGs. The MP40/STEN fires at 540 RPM or 9 RPS while the StG 44, the second slowest firing assault rifle, fires at 600 RPM or 10 RPS. That is a 100ms difference in TTK already there. ARs also get access to hipfire accuracy improving specs so their hipfire ain't that far apart from the SMGs. At 5 or 10 meters, the chance of you missing your hipfire is almost zero. If you truly want to lead ahead with the SMGs, the choices you have really are the MP28, the ZK-383, the M1928A1 and the Suomi. They perform significantly better than their equal rate of fire ARs at the SMGs' optimal range due to generally bigger magazine sizes and hipfire.
AR hipfire is always worse than SMG hipfire. Upgraded AR has about 10 meters. hipfire range, base SMG about 15 meters and upgraded SMG around 20 meters. For headshots, those ranges are about half. Getting the hipfire upgrade on the StG also stops you from getting the ADS upgrades. On the MP40 you could get the ADS upgrades, still have better hipfire and make up some for the raw damage output disadvantage you have, particularly beyond 30 meters. The hipfire upgrade is not free and has a clear performance downside at medium range.
Within 30 meters, the raw TTK disadvantage of the MP40 or STEN against the StG is 33 ms. Zoom in advantage can be as high as 266 ms, although 66 to 100 ms is more common. Sprint to fire advantage is 66 ms.
Between 30 and 50 meters, raw TTK disadvantage is 150 ms. Effectively less if the StG has the hipfire upgrade and the SMG comes with the ADS upgrades. You will lose most perfectly even 1v1s. But if you have 100-200 ms of a drop on somebody, it will be tied or slightly in favor of the SMG, depending on if the AR is already ADS and if not, how fast it goes ADS. It is past 50 meters where SMGs really suffer because the lower bullet velocity starts making it hard to hit moving targets and the raw TTK disadvantage grows up to 266 ms at 75 meters.
With the faster firing SMGs, you'll miss out on a lot of opportunities past 20 meters. You get close range dominance, but you don't need more than an MP40 or EMP to beat most ARs and LMGs up close, if you hipfire them well. Only the 1907 might require a bit more ROF to duel.