( I very much hope this aspect is mirrored in game 2 )
Whether you have beaten the game a senseless amount of times, are looking for something interesting or new to try, I think that HG's potential is not being seen as much as I would like it to be, at least in the subreddit and discord win screen pools I check in on from time to time.
If Mag Spring, Caliber Reduction, Ammo TP, or any sort of series of mag capacity upgrades are able to be carried into the later stages of the game for your preferred weapon, and you select Ammo Gain upgrades over everything else with exceptions, you can essentially turn any weapon you find into never needing to reload via onslaught system in-mag ammo regen.
This, combined with the power upgrades of Hyperfeed, Twin Link, Target Cogitator, Onslaught System, Magic Mag, and anything else you can imagine, is a neverendingly enjoyable cycle that seems to surprise me over and over again. I've done it and had success over any other builds so far with HG, even getting into the Loop 2~ areas as a moderately veteran player.
It goes beautifully with healing upgrades as well, because HG heals on bullet hit, doubled during onslaught.
If you decide to try this, my top weapons are the RRX Coil Shotgun, KI Vector, Bren, M202 Flash, and so forth. Guns that you might not think could be good that have manageable heat and an expandable base mag size.
Try to look for pierce and reducer too. I don't think HG really functions the best with LMG's in the game ironically because at some point that damage potential starts to be useless versus high speed, instant firing enemies in the loop so you have to compromise with a less daunting weapon to the MS statistic if you want the game to be more interesting than refractor crystal. 🙂
I know this post is a few days old, but I can totally agree with OP. I think Heavygunner as he is deserves to be mirrored in the second game. He is a bullet machine, whether it's the basic LG or another gun, it feels like his perfect calling is a bullet storm, an unending unyielding force of lead and shells. He won't get anywhere fast but he will get there with molten piles of scrap and oil being left in his wake. Playing him and using the methods described just feels good. There can be planning and forethought in carrying jammed weapons and saving them to unleash sometimes 20+ seconds of the Onslaught System, which is just a grand feeling. Sure other classes may feel great as well, dealing large burst damage, or cosplaying engineer TF2, being stealthy and calculated, or demo being complete madness with explosions in some cases; But Heavygunner is simple, yet so complex. OP outlined an amazing aspect of him and there are so many others as well, and this isn't even mentioning max fire-rate playstyle. Heavygunner is amazing in his current state, and I would love for him to be polished up a bit, but I feel mechanically he is an absolute treat. I have high hopes for him in Synthetik2, and if he is already a treat in his current state, then if done properly and paid proper homage, he could easily be a dream come true.
-Your local Heavygunner one-trick
Using coil gun with HG ammo reg build is a pretty smart idea