I'm totally onboard with the balance considerations mentioned above, but it's worth mentioning that one paradox it creates is that firing your assault rifle in consecutive SA-bursts, (3 rounds per IP) accumulates recoil, while switching to FA and putting out 6 round bursts constantly does not.
You know, that is how it work in real life as well....
If you have a SA weapon and pull the trigger over and over and over you never take the time to recover the recoil and eventually your aim goes to shit due to fatigue in your arm, vertical kick from the weapon or whatever (depending on how wired you are the time between each round will be 0.375 to 0.75 seconds)
If you have a FA weapon and pull the trigger for a short burst (6 bullets take 0.3 - 0.5 seconds to fire, depending on your rate of fire) and then spend the rest of the action phase not shooting - then you don't suffer from the recoil when you decide to pull the trigger again in the next action phase (depending on how wired you are that would give you a pause between bullets of about 1.1 to 2.6 seconds -
or 3 times as long time to recover recoil between bullets compared to the semi-automatic burst example above).
If you have a SA weapon (or BF weapon) and pull the trigger only once and then spend time not shooting (recovering recoil) for at least a simple action you will also not suffer progressive recoil between your shots (depending on how wired you are that would give you a pause between bullets of 1.5 to 3.0 seconds (or 1.3 to 2.8 seconds for BF) -
again more than 3 times as long time to recover recoil between bullets compared to the semi-automatic burst example above).
Sniper rifles normally have higher base damage value, base accuracy and armor penetration compared to assault rifles.
Shotguns normally have comparable accuracy but a lot higher base damage value and higher armor penetration compared to SMGs.
Heavy Pistols normally have higher damage value, accuracy and armor penetration value compared to MPs.
Against single extra high armored targets with low defense pool (or no defense pool because they are unaware or surprised) SA weapons often come out ahead. Against single extra high dodge targets FA weapons often come out ahead.
One thing to note about FA weapons is that while it is very possible -it is not trivial- to reach 6 points of recoil compensation. It is even harder to reach 10 points of recoil compensation for moments when you really want to spend the whole action phase doing nothing but shooting bullets (you basically need to invest into strength, replace the sound suppressor for a gasvent, go all out obvious with a gyromount or use one of the few FA weapons that come with a lot of custom built in recoil compensation). Another issue is that you burn ammo faster. Most FA weapons run dry after just 5-6 short bursts. Your players probably have a few extra clips but GMs do (or at least should) put a limit on what you realistically can carry with you.
The difference of using SA weapon over a FA weapon against multiple targets is that you can use a SA weapon against up to three different targets that does not even have to be standing next to each other (but they do need to be at short or medium range as described on p.167 and you need to have a weapon skill of 5+ as described on p.196) while a FA weapon can be used for area of denial by spray n pray a frontal cone area (but this will affect both friends and foe in the area of effect, described on p.179). Both with their different Pros and Cons.
As I see it SA weapons are better suited for skilled and agile (but possible not very strong) sharpshooters while FA weapons are better suited for big and strong (but possible not very agile) commandos.