Delves are a great way to gear alts, Honestly they’re a great way to gear mains paired with raiding. The Adventure level gear you can buy from the Delve shop keeper prices are atrociously overpriced for how fast you will end up replacing that gear. Not to mention you have to complete the Delver Journey to even unlock that gear.
For instance I kill Zek’Vir (?) on 5 alts 8 times a week for vault slots, not to include the bountifuls i use up and i have barely made it to the final 3 Rewards on that path.
Make Coffer keys Warbound transferable, the Undercoin is Transferrable which can be used to buy the keys anyways.