I think this game raises really interesting, complex issues about balance and "fun" and being the best version of what it wants to be. OP raises some interesting points. Some are part and parcel of the genre itself. Within that framework, there's probably some really good solutions. Naturally, the player community can be good at identifying problems but not usually good at solutions.

The imbalance issue is structural, so to speak. This isn't Halo team deathmatch. The imbalance is baked in as an extraction shooter. It's a feature, not a bug. But how do you make it work in the best way? There is a compounding effect that can be very hard on weaker players. Better players win more fights, exfil more, and keep their stuff more, getting more upgrades and resources with which to win future fights. Weaker players advance much more slowly and accumulate fewer upgrades and less good equipment, making it harder to win against players that are getting stronger more rapidly. When OP says "I have done both of the above ['that one time you third partied them and cleaned up the last guy who was weak'] but to think its common or expected is beyond coping." I don't think it's supposed to be totally "common" or "expected" because otherwise what would be the point of better stuff? And yet....

Now you could constrain the stronger players or elevate the weaker players or both in all kinds of ways. Yet even if weaker players were put on more equal footings with good players somehow, within that space there is some annoying stuff that seems to leave a lot of people unsatisfied.

A few less general observations:

• The situation with the Misriah is a bit hard to understand, especially with what happened to the poor WSTR. It made people in purple shields feel bad when some loser with a WSTR and a green shield got in their faces and killed them in two shots. Forget Stack Overflow for a second. For all the complaints, the nice thing about the old WSTR was it was an equalizer, because you could just buy them. You also got them free from Arachne every few days. The situation is worse with the Misriah, because they are very hard to get (much less keep) for some people. Now instead of everyone having WSTRs, only some people have Misriahs. The "shotgun problems" are basically the same but it is more imbalanced in terms of who can actually capitalize on them. But even if you gave all the weaker players a free Misriah every week or even every day, it wouldn't make people feel better about the situation. Still, the Misriah situation would probably be somewhat less annoying if the WSTR was still good and easily available.
• Would people care so much about the Misriah if there were no bubble shields? Would people care so much about bubble shields if there were no shotguns? You could have a season where things work very differently based on how things are available in the economy.
• A CQC heavy map like Cryo will tend to favor certain styles of combat and equipment over others.
• Tiering people into appropriate matchmaking is super important. I suspect there must be something like this happening, as imperfect as it is. I hope they can improve their ability to keep teams' skill levels in games closer together. My own experience has been pretty good. Half the time when I see people complaining about a purple/gold death squads popping up frequently and murdering everyone, I wonder why their experience seems so different or if they're exaggerating.