A card system
The reason for this idea, this game needs more gold sinks. This adds an RNG eliminate which can make the game more intresting and this adds depth to the game without complexity.
A card system where you can give your players a card to affect their performance or change their stats.
The reason I mentioned as a gold sink is, since this is an MMO of sorts, it runs a huge risk of hyper-inflation. Having more options to dump money out of the game can be worth it. Just for context you pay with ingame currency.
For the RNG eliminate, a lot or MobaManager is fixed and ridged, with little change. I know when I log in what to expect. Having an RNG eliminate, especially a minigame of such gives excitement.
For the depth vs complexity idea. This game is very complex, with lots of prerequisite knowledge before you can play effectively even with it's depth (the diffrent ways a player approaches a challenge). A card system can be very self explanatory without extra complexity added ontop but offers more options for playes to tackle problems.
So to the refined idea.
Every day a player can invest money into a system, simlar to the scouting, however they receive a card in return. This is a random card of a random effect but they can only hold onto a limited number of cards, maybe 10 or so. Cards can be sold back to the game for a substantialy lower price or sold on a transfer market.
The cards themselves effects could range from +1% energy recovery for a single player to a underdog bonus for your whole team or a +5% streaming bonus. There could even be cards such as +1 adc skill or to switch 10 of your Support skill to technique.
Each card can be used only once and only takes 1 card can be used per player per day. The idea is low value cards such as energy regen and maybe small performance bonuses are common while big effect cards are super rare, such as the stat adjusters.
Since there is a transfer market for these cards, there is a way to resell unwanted cards and purchase high end cards. I would estimate the value of a +1 energy card to be around $5000, while a +5 stats could fetch €5m+ with the right buyer.
I would say a good initial investment would be around $20'000 for a card, the idea being it's risk vs reward for using it. Maybe the cost can scale up.