I’ve been doing this a while too. The farming I do is with:
Fortress Gate
Lady Sapphira
Valkyrie
Tyri
Then you fight on the Fortress Siege challenge at Broken Spire.
The basic strategy is that between the two Fortress Gates in the first slot on both teams, you can completely ignore skulls. Tyri can either feed herself or Lady Sapphira until the Archon and Terraxis are dead (Terraxis first), and then she just feeds herself. Lady Sapphira could easily be swapped out for another single non-random targeted true damage troop.
The Valkyrie is partially there for Necromancy but mostly to generate a bunch of souls and to clear a bunch of gems in one go towards the end when I’m trying to cycle the board to Tyri’s colors.
Then I just keep track of the number of maps and once I hit the cap (10) I kill the opposing Fortress Gate with Sapphira. And since it’s true damage I don’t have to care about all the casts of Reinforce it’s been making. Between difficulty & spider armor I hit a caps of 90 souls, 220 gold and 10 maps.