As a keyboard/mouse multiplayer rushing nerd scavenging the TeamDeathMatch, my go-to weapon is the KSV smg.
It’s a bit less effective than a PP-919 on mid/long ranges, or than a Jackal (faster ADS) and Kompakt (rate of fire) on short ranges, but I find it to be the most versatile “and” with an ironsight that suits me the best.
I’d like to give more credit to the Jackal, especially since it’s “the” smg in ranked (KSV not available unfortunately), but I’m not a big fan of its ironsight 
..
Here are the loadouts that I use the most :
STANDARD - Using the gunfighter wildcard to make the most of my KSV, I tend to use this one a lot if the game starts and could be sweaty :
…with the following accessories :
As a solo player, I’m used to fill-in teams that are losing and join them mid-games. Usually, some UAV is running permanently (and ennemies are probably running scout pulses as well); so it’s time to pull my ninja/ghost/silencer/shadow loadout :
In lobbies w/ high SBMM that really helps as players are used to chek very often their mini-maps.
On the opposite, if the lobby is pretty average and I feel I don’t need to pay too much attention to my positioning and all, I go with a more agressive setup using this one:
These are my go-to setup that I almost exclusively play now since I’m a master prestige on Black Ops 6. These are my stats, playing solo in standard TDM w/. a pretty sweaty SBMM :
As I mentioned before I often fill-in a blank spot for leavers, but sometimes it’s actually my whole team leaving (as I’m sure it happens to you as well from time to time), and that last game (from yesterday actually) is a good example where clearly the balance was completely off, w/ only me and one teammate remaning for 1/4 of the game :
But that good old KSV did the job 
How about your setup ?