This has been said a million times over (probably) but take a look at Digital Extremes’ game “Warframe.” With Free DLC and free event, an endgame that may seem lacking, but an array of unique builds, a plethora of weapons and several different characters.
While yes Destiny may not be as big, or may not have the backbone to support something that big (for some reason) they CAN follow the same marketing stunt.
You want Micro transactions? Fine, but make your DLC free then. Well Call of Duty has both, that’s Call of Duty, they have a larger community, and while the gameplay and “fun-factor,” of the game is highly opinionated, the game built that structure. They’re marketing is “Hey it’s an online shooter, that’s it, no PVE (not counting Zombies), just straight online shoot em up.” They don’t have to worry about loot boxes or anything like that because the player base knows, they are getting what they paid for. Blizzards Overwatch is the same, yes their DLC is free, but it’s a shoot em up and that’s it, loot boxes work for those games.
Your game is not a shoot em up, by any means. You have a game acting like an rpg, with an online infrastructure, you have an arena not an actual PvP. With no private matches, custom game modes, or even the option to choose a game mode type, what makes you think you have the right to copy the big dogs?
Destiny 2 is currently a teen figuring out their place in the world, and instead of the teen growing to a promising future, it is leading to a dark long journey of horror. You can do micro transactions and paid DLC no one could honestly care, it’s when you’re marketed as an fpsrpg with no context besides everything hidden through an RNG paywall, is when people get irritated.
Warframe does kinda do its f2p model well, and I'm not sure I entirely have the words as to why. Content is very nearly monthly, and free. I'd hazard to say that 60% of cosmetics can be earned, and 100% of practical things like guns and characters can be earned, some with different degrees of ease but that's beside the point, it is a grind game. There's practically no loot box mechanic at all, or any RNG based paywalling (with one exception of 'mod packs' that contain some mods, but I've not met anyone who feels this is an issue- just everyone sees it as bad value).
900 odd hours in, if you want a recommendation I would go take a look. F2p, so you won't lose anything really. I would advise using google or the wikia for a while though, there's not much tutorial