Well, part of the reason you can't get large numbers of setback dice is because the designers deliberately designed the rules that way, with Sam Stewart flat out saying the made the change to cover during the EotE Beta simply to cut down on the number of setback dice applied from things like armor and cover.
Defensive Training only seems lackluster when using two very specific lightsaber attachments (curved hilt and Lorrdian Gemstone). And then only if you don't invest in Defensive Training, which if a PC is going to focus on being a lightsaber duelist, they'll have plenty of chances to do as said talent shows up in four of the LS Form specs (twice in Niman), and with the exception of Makashi Duelist is fairly easy to work around if you really don't want the talent.
That's not to say I don't think it could use a little sprucing up; thus the suggestion to have it operate similar to the Unrelenting Skeptic talent only applying Threat instead of Failure, though perhaps some cost should be applied to said revamp of Defensive Training as it wouldn't be too hard to stack ranks of it, and thus make triggering effects that rely upon the attacker generating lots of threat (like Improved Parry and Improved Reflect), which some GMs may not be comfortable with.