Well, after two days of ascendant shards from the queen's wrath combined with about 12 dropped in the vault of glass, I was able to fully upgrade all my legendary and exotic armor.
Besides, the loot cave wouldn't be any help in upgrading legendary gear.
First, dismantling Queen's Wrath items for shards is out, they patched that too. Second with no matchmaking for the Vault of Glass, I can't play it. I only have 2 friends that play the game so it's not an option. And third, using the Loot Cave I was able to farm enough shards by getting a few as random drops and breaking down a few legendaries I didn't need.