Thorim may seem to have a ‘godly’ power because he can select a Tier 7 minion but you constantly get a choice of 3 trash minions that cannot synergize with the tribes in the BG.
The T7 minions simply aren’t powerful enough to warrant such a long wait to play them.
Solution: offer the choice multiple times so that when you can play them you can drop multiple T7s or sell them to discover 3 T6.