I use Mesa with corrosive regulators (with all possible fire rate mods and R5 Arcane Velocity) to cheese the lich. Or when I am bored with mesa, I use Revenent's Reave to deplete shield of lich. Also using khora for defense is a good option, I rarely use it but Khora hits like a truck. However, if you need any help for lich farming ping me in game. It is the same username.