The gap is not very huge Force-wise, but it's there, especially in mastery, variety, exotic abilities and stuff like that. In terms of dueling capacity there's a pretty clear space between them.
There are some areas in which they are even, some in which Caedus sports a minimal edge, and some in which Caedus is visibly superior. Caedus would win 10/10 against Vader, even though with great difficulty.
team 2.
Caedus is still a greater duelist than Vader, even if you don't want to debate the force round. Stomping Katarn within seconds to the point where he needed intervention from his students, fighting evenly with an amped Jaina (She needed help), are all feats that surpass fighting evenly with ROTJ Luke/beating Galen/beating Ahsoka/Vader's technical mastery. Sidious is powerful enough to hold his own against Luke, whereas Vader will die to his grandson every time in a lightsaber duel