Arcann/Ulic Qel Droma vs. Ahsoka Tano (Rebels)/Ben Kenobi
(sabers only)
Who wins
__________________ "Happiness is a lie. Life is horror. The light is always dying all across the universe. The last star will flicker out someday, when it does, all that remains is shadow. And I will be its king!"'-Amahl Farouk
Ben is superior to his ROTS self. Ahsoka has contended with Vader, Ben's equal, on a ds nexus and hence can be assumed to be close with him.
Being generous, as TCW Kenobi has fought evenly with TCW Maul, it's fair to assume ROTS Kenobi and SOD Maul are on the same level as duelists.
TCW Maul's inferior version has decisively handled Qui-Gon Jinn, who has multiple staements placing him as one of the most skilled jedi in history.
Even with this incredibly nerfed scaing I've scaling the two so that I don't have to get into another repetitive argument about Rebels Maul or Maul's performances vs Kenobi we still get the following line of scaling:
Ben>ROTS Kenobi~SOD Maul>TPM Maul>One of the best swordsmen in history
and:
Ben >~ Ahsoka> ROTS Kenobi ~ SOD Maul >TPM Maul >One of the best duelists in history
Even setting aside the aforementioned points of contention, that's still multiple levels of scaling above the best duelists in history. That's not something either Arcann or Ulic have anything as impressive as.
Arcann and Ulic's multiple levels of in-era scaling isn't more impressive than multiple levels of scaling above force user who have sh!t that can be applied across eras.
That's about as relevant a comparison you can draw between two characters in separate eras regarding a saber only confrontation.