Even if you just get bored and wanna battle without risk.
That's why I'm trying to contribute.
what if you could create trainers in survival, and give them your pokemon? Basically make an NPC version of the Ranch Block.
This would allow you to battle your own pokemon, AND add the ability to use the trainers as guards for your base, or whatever.
If they also add a way to let npc trainers distinguish between friend and foe, so that a trainer only attacks other players, or players that do/dont fulfill certain conditions, like wether they are on their bosses friendlist or wear certain equipment, like, if you wear a team magma hat...
Also one could make them follow the player, to act as double battle partners, like in some areas of the actual games (gen3 onward).
I don't think we need to overthink balancing the exp though.
• a number of gyms scale level to the challenger anyway
• secret bases were used in ORAS to turbo-grind exp via pokemon that yield high exp amounts.
if anything, maybe we need to make legends and whatnot scale to the player in this case, with a minimum level set so they don't scale too low.