As someone who didn’t go Peltasta on my last swordie in favor of a more “pure DPS” centric build ( one of my main regrets ), I’d say that taking it is a really good idea. Since the game is mostly centered around doing missions and dungeons now, a single rank in Peltasta is incredibly useful. I often felt that I didn’t have a true role in parties as a swordsman because I didn’t have a rank in Peltasta, and noticed how much easier dungeon runs went when we had someone that did take a rank in it. So definitely keep it 
The taunt will always be useful in parties, and since you have the mobility of a cataphract, you will have an easy time moving mobs around. Also the knockback attribute on umbo blow is very nice in PvP. Having the ability to block during boss fights to avoid getting knocked down ( while pain barrier is on cooldown ) so that you can effectively move the boss around is really helpful as well. Bosses just relentlessly spam knockdowns now, and being able to control a boss for your party is invaluable.
This build is pretty standard, and it works very well. Especially with the recent buffs to cata, going cata3 is a pretty solid choice now. I would move some of the points around a bit though.
For Peltasta you definitely want max Swash Buckling as it’s your MvP skill, and you only want Guardian level 1 for the evasion attribute ( +18% evasion ), as the more you level Guardian, the more attack you lose ( the +defense tradeoff is poor ).
On Cataphract I would really figure out a way to get max Rush instead of taking 3 points in it. You could take 1 point out of Trot and Doom Spike, or 2 points out of Trot. Some people don’t even take Steed Charge too. Up to you.