That'd be nice if we didn't already know that, in his era, Ulic was second only to Exar Kun in practically every relevant field.
There's also the fact that the spirit of Nadd, taunting Ulic, refers to him as one of the "great ones." Then he references Exar Kun, saying, "And there is another, even greater than you."
Aleema says that she "senses the Force is strong (in Ulic)."
When Satal injected Ulic with Sith poison, Ulic's force-powered response was enough to wreck the torture droid he was strapped into, much of which was made out of stone. It was described by the narrator as, "A massive impulse of Force energy that blasts the young Jedi free of the droid's embrace"
When Ulic blasts his friends back after defeating Satal Keto, it's described by the narrator thusly: "But the process that has begun in Ulic builds to catastrophic levels... unleashing waves of dark side energy in his body and against his friends!" The panel shows Ulic in the center and a visible blast of energy knocking back Cay Qel-Droma and Tott Doneeta.
When Kun is crowned and Ulic named his foremost apprentice, the narrator describes their joined power from Aleema's perspective: "As Aleema regains consciousness, she beholds an astonishing transformation in her lover Ulic... Ulic Qel-Droma and the intruder (Kun) are rippling with Dark-Side energy... more power than all her Sith magic has given her."
Anyway, your assumption that Ulic is mediocre in the Force is unfounded. His skill with the lightsaber over both opponents is great, and at the very least he is equal to both of them in Force combat.