I've been in the circles that believed in its existence (and played around with it) before the confirmation by the devs. I think acknowledging it officially was a big mistake, as players will now focus on playing the game system instead of enjoying the gameplay.
On ABMM itself, I really like that data about players' actions in raids can be used to distribute lobbies. I think Embark should lean towards providing a balanced experience (looting with the fear of what could happen with another raider) rather than putting people with the same "rating" together. We don't know what their approach is so no way to be more specific about what works and what doesn't.
I do think solo and squad ABMM should be separate, currently it does not feel like it's the case.
An experiment I ran myself: after playing squads with friends, which is always PVP heavy, I tend to run a bunch of naked runs (free loadouts dont give you a safe pocket, but going with absolutely no gear does) and run around maps.
This allows me to first learn the maps (locations and loot spots) and how to traverse them better, complete quests I've put off, and skew my matchmaking towards friendlier lobbies. I've had people completely ignore me, others chatting, a guy dropped a blueprint before going away... And the few that shoot and kill me end up disappointed by seeing zero loot.
It's my first extraction shooter as well, I've slowly accepted to not care too much about gear.
I don't know how to explain but you'll reach a point where you see that gear is just a bunch of resources needed to be crafted, and those resources can be easily gained through recycling, buying from traders, or from Scrappy.
This means my level 4 Anvil is actually just [x components + y coins] instead of a gun, a Raider Hatch key is 66 Seeds, and so on. If I lose them, I probably already have the resources to get new ones, or I just need to do cheap, chill runs grabbing anything to recycle once I'm back.
This alleviates gear fear and combats frustration when you get knocked out and lose it all. I tell myself "you win some you lose some". Another thing that helps is keeping in mind that you only lose what you brought with you, the loot you carry is never yours until you return to Speranza!