HoH:TL writes (p.125): "Magi of Tremere usually desire to be excellent duelists, which means they specialize in four arts [2 Forms and 2 Techniques seems implied]. This is because the other party in a duel can veto their rival’s first choice of form or technique."
This makes little sense. Specializing in two Arts and two Techniques is a poor strategy for a Tremere duelist. A Tremere generalist, who spreads his xps evenly among all 15 Arts, is almost always going to be more effective for the same number of xps (and note that lower scores are generally easier to raise -- i.e. get more xps/season -- than higher ones). A slightly better choice would be to spread xps among 13 Arts, avoiding one Technique and one Form, and placing slightly more xps in each of the Techniques (a good rule of thumb is to divide the xps by 14, with each of the 13 Arts getting one "share", and the final "share" divided evenly among the Techniques).
Check it out.
At Gauntlet, a "standard" Tremere with 120 xps spread evenly among 4 arts has a score of 7(2) in each (and 0 in every other Art). In a duel, he'll likely get one high Art (Form or Technique, depending on whether he's challenging or challenged) and one low Art. His final Arts scores will be 7/0; his Focus is useless since the lowest Art is 0.
At Gauntlet, a "generalist" Tremere with 120 xp spread evenly among 15 arts has a score of 3(2) in each. In a duel, one of the two Arts is doubled by his Focus. Thus, his final Arts scores will be 6/3, which is somewhat better than 7/0.
At Gauntlet a "13 Art" Tremere with 120 xp would get 8 to 9 xps in each Form (about 120/14=8.5 on average) and 10 to 11 xps in each Technique (about 120/14 * (5/4)=10.7). He would then have a score of 4 or 4(1) in all but one of his Techniques, and a score of 3(2) or 3(3) in all but one of his Forms. Vetoing the opponent should he choose one of the two weak Arts, the Tremere final Art scores will be 6/4, slighly better than 6/3 and a certainly better than 7/0.
Let's now look a magus 4 decades after Gauntlet, who's spent half of his seasons studying Arts (so 30xps/2 years). Such a magus has 120+30*20=720xp Art xps. It's not difficult to see that the "standard" Tremere ends up with a score of 18(9) in his specialties, bringing to a duel an 18/0 Art pair. A "generalist" Tremere has a score of 9(3) in each Art, wielding an Art pair of 18/9, much better than an 18/0. A "13 Art" Tremere has a score of 9(6-7) in his "good" Forms and a score of 10(10-11) in his "good" Arts, bringing an 18/10 to the duel -- again, very slightly better than the "generalist" and much better than the "standard" Tremere.
Finally, let's look at an Archmagus a century and a half old with 2000 xps in his Arts. The "standard" Tremere brings to a duel a 31/0 Art pair. The "generalist" brings to the duel a 30/15 pair. The "13 Art" Tremere brings a 32/18 pair.