Ok I'll try not to get too heated with this as most of the lads who know me know my stance on this subject

HMG,
A: No.
B: The HMG has been through a great deal of nerfs since I began last June when it really was an HMG. Since then the range has been decreased from 75m to 50m , RPM has been decreased from 3000 to 2000, damage for the basic HMG was decreased from 19 to 16 and heat buildup increased. I would also like to note that the current version has actually been buffed because in the last build the heat buildup was nearly 2x what it is now and the RPM was only 1500. So IMO the current version has been through the works and is actually pretty good balance wise. A lot of the Anti HMG comments came from the large influx of new players who haven't seen how much more effective higher end assault gear is than higher end heavy gear and were probably worried about a heavy fest later on, chill lads it's slowly balancing out
C: The weapons main flaw is part of it's strength being mounted on a heavy suit which means slow speed in all areas although high armour, no equipment slot so no spare ammo and very limited slots. I did find the fact that the spread get's tighter interesting however with the low damage, especially at range, it can actually work against you if you use the weapon in a area denial role as you can't keep the fire on enough people to hold them unless you control the choke point in the first place.
D: My play style can sometimes counter the weapons flaws by controlling the terrain I fight in however I am far from a hardcore gamer and the HMG allows me to fight effectively even though I'm tired from work and can't aim for toffee. So it also gives player who are new or have less than stellar reactions a viable option, this is why I feel the HMG kinda levels off a bit in the stat dept towards the high end gear so as to try and get the gamers to jump to something new when they find they're levelling off in the heavy area.
E: A good weapon to compare the HMG to would be the AR actually, it's fairly easy to use and does good damage I think 33 per shot??? so only about 20% less DPS compared to the HMG which can be easily buffed up to compete with it. The AR reloads and aims a lot quicker and can be mounted on a far more mobile suit which I think offsets the damage output of the HMG and there is a far better improvement of stats of the AR and Assault suits as you level up compared to heavy gear.
F: Ok the one weapon that really shines against the HMG is the Laser rifle hands down. I hate seeing that green beam of death swinging my way but it is very effective as like the HMG the longer it's fired the better it is (depending on situation) and considering the fact it can be mounted on even a scout gives it far more flexibility as an area denial weapon on open ground.
G: Erm wait and see what happens on the next update, as you could see the HMG wielding heavy become a dinosaur like the missile tank if it gets another nerf and with the new weapons coming out you may need that HMG even more than you thought???

SG,
A: No.
B: The SG does what it says on the tin, always has which is nice for a change. Also it gives people who want to be a speed class an effective weapon at close range but forces them to get close as well making the game more balanced.
C: The weapons main flaw is its range and mag capacity also the higher end versions don't offer much improvement over the basic models from what I have seen.
D: I need to be really in the zone to use this weapon and I don't really use it too often because of this but the guys who do are very good. The key is much like the HMG heavy, control the terrain don't fight in open ground where they can see you coming but use your head and flank or out pace your enemy.
E: A good weapon to compare the the SG with would be the Mass drive IMO. Mainly because you need to know it's limit's (SG range and MD it's arc and blast radius) also there's not much ammo for either weapons and while the MD is less specialised I think it's comparable.
F: AR is the best counter for a SG as you outrange him by miles have a big mag and higher DPS at range while still being in a fairly quick suit allowing you to keep up with the enemy.
G: As above wait till the update before asking for any sweeping changes as you might find the need for all of a weapons capabilities to counter a newer threat.

As you can see I do favour the HMG but trust me not nearly as much as my FG for tank killing. However I'm going to start skilling into Scout suits so I have a mobile fit for corp matches which are miles from pub matches where people come to you and you just mow them down with the HMG. In my latest corp fights I always find myself being outpaced by the other team and I think this is a trend which will continue into the pub matches as it did in the previous builds thus diminishing the role of the heavy, I know I'm using it less now.

Regards

Snag

No, by damage per round, the HMG is firing a smaller round than the SMG, at twice the fire rate. It has just over twice the optimal range of the SMG so it's charge would be a bit larger. If an operator is able to fire the SMG easily then a massively armored dropsuit like the heavy would be well able to handle the HMG recoil.

And there aren't barrels spinning in different directions. There's a weighed collar that spins to create a counter gyroscopic force, that combined with the gyroscopic force of the barrel group makes it a very stable platform. In real life this collar would just prevent the tendency of the gun to slightly pull to one side at the start of firing.

Again in real life, infantry operated miniguns mostly operate off pintle mounts. Look up YouTube for any number of videos showing how stable and accurate this is.

Fair enough, this is not real life, so designs/changes don't necessarily have to follow physical laws as we know them.

As to peoples accusations of the heavy having pin point accuracy with massive range beyond the AR, create an alt character and try it out. You'll soon be eating your words. When a heavy might be wasting ammo and tickling you at long range, they might very well have a team mate tearing you up with an AR, but manage to get the killing shot. The HMG is useless at long range. One lad up above saying 80m. Come off it. Try the setup out first so ya don't have to pretend as to the facts. Yes, the assault version has a max range of 80m but it's cone of fire is massive at that range.

As to the OP wanting to know our thoughts on HMGs and SG, Snagman 313 puts it more or less as I think. Being lazy, I won't type it out again.