This is so spot on man. The game is solo-hostile full stop.The biggest thing holding Mortal 2 back is that solo-play is not competitive in any-way and the game is almost unplayable as a solo-player unless you play very specific meta mounted builds and even then your access to end-game content will only include trolls that are uncontested. Until the community drops its bias and is willing to admit the importance of solo-play to the population the game will continue to suffer until its eventual death.
Lets take a look at the examples of how the other much more successful full-loot mmorpgs approach solo-play and balancing it.
Albion online: Avoidance mechanics- Solo players rarely have to take fights if they don't want to. Also corrupted dungeons ( areas with forced 1v1s) is among the most popular content in the game.
OSRS: Avoidance mechanics (teleports) and areas with forced 1v1s. Most end-game PVE is solo-friendly.
Eve: Avoidance mechanics(cloaks)(nullifiers)(Cynos), most end-game PVE is solo friendly. Areas with forced 1v1s.
Why do all these games have avoidance mechanics in common and how does it directly affect their population metrics? Because avoidance mechanics are the best anti-zerg mechanic you can implement. It is simply put the most balanced way to deal with unfair gameplay. It forces people to offer "good fights" or they get "no fights". Your only other option for balanced solo-play is to make people so strong that they start 1 shotting eachother which is why games like RUST/Tarkov have population. You either need to give the solo player a way to win the fight occasionally or avoid the fight usually(if they choose to do so).
Those are your only two options if you wish to have a populated full-loot MMO experience.
"Most" people will not play an unfair game environment, even if that game fun otherwise. Which is exactly where MO2 sits right now. They simply opt-out when they feel they can't be competitive. Obviously not every fight will be consensual, in EVE you are limited to very few ships if you wish to fully avoid fights, in OSRS you will eventually get caught with a teleblock and be forced to fight, and in Albion you will eventually get caught and dismounted. But the important part is that in all of those games...for the most part...the PVP is consensual, even if it doesn't feel that way to the players playing the game.
Although another huge thing is the lack of understanding of mechanics design and implementation in general.