With the current state of the game, one farms goblins for 2 out 3 months of each season, almost exclusively.
My suggestion: Shift some of the time a player spends in game from goblin farming to gear/rune farming.
In order to do that I suggest each goblin run to give 4-5x the amount of exp pots, each domain to give 3-4x the amount of shards.
"But why does it matter where you spend your time whether it's goblins or dungeons?" - I think this could let many of us experience team building more freely, essentially letting us level heroes and try different teams while also reducing the amount of fatigue of running only goblins for the majority of each season. I think most players will also find it a bit more exciting running dungeons in the hope of getting that insane and extremely rare piece of gear with good sub-stat rolls.
Another approach to this issue by @formal crescent: Time gated scaling locked exp. Units already leveled in previous seasons retain their exp and simply scale up with the time gates in the new season. Players only ever have to level NEW units they pull.
TL;DR - I suggest to 4-5x the amount of exp gained from goblins & 3-4x domain shards, so players can spend their stamina on dungeons instead, then we get to do something else but running goblins 2 months out of every season.