From what I have seen after the Forsaken update, regarding the time to kill for auto rifles and sub-machines, they haven't had the body shot damage correctly scaled. In Destiny 2 Year 1, the auto rifles and sub-machine guns had about a 30% critical multiplier and not a 60% critical multiplier. For example, the Ghost Primus, a 600 rpm auto rifle, in the Crucible at optimal range, did 17 damage to the head and 13 to the body (about a 30% difference). Enter the Forsaken time to kill update and it does 21 to the head but still only 13 to the body. I further believe this to be an over sight because on the Destiny 2 combat reveal stream (https://www.youtube.com/watch?v=fdylZ_1Vj-M&t=1180s) at 41:08 Cozmo used the Ether Doctor (a 600 rpm auto rifle) and said "even with the body shots, you can see a difference" when in truth there was no difference in body shot damage from Year 1 to Year 2. I believe the change to make auto rifles do 30% critical damage instead of 60% and to have their body shot damage increased was in Destiny 1 Rise of Iron, because auto rifles were harder to land consistent head shots compared to the other primaries. This was grandfathered in Destiny 2 Year 1 with the auto and sub-machine guns and it would be greatly appreciated if it went back to that especially for sub-machine guns.
Handcannons and pulse rifles outshine autos consistently in crucible because they are peek weapons, there is no such thing as peeking with an auto rifle. In order to match, auto rifles would need to be buffed as you said
Auto firing weapons such as ARs and SMGs need to have a buffed body shot damage imo. It's hard to hit consistent crits with them, and that's what they need to be competative. They need to be the most consistent weapons, but not outshine those that are more rewarding on skill. I feel they need to be the 'noob friendly' weapons, if that's a decent way of putting it. This is also taking into account that you need to have your whole body exposed to get optimal ttk. With HCs you can peak in and out of cover. It's a difficult topic because you dont want to make them op. Like D1. Bungie will most likely address them eventually once the meta starts to really settle down.
Having to get precision shots with SMG's that fire all over the place is a bit silly but for auto rifles in general I think it's a decent change. Even with the fastest firing auto rifles I can still land enough crits and body damage to down an opponent in a decent enough time. A problem I see often is pulse rifles and handcannons out-damaging auto rifles and 1v1 encounters (rare but they do happen) feel lopsided. SMG's have the issue of Am I Close Enough Or Too Close? Shotguns have good range but some of them have ALOT of range. Trying to put out enough damage from an SMG before they close the gap is practically impossible at this point.