I'd be much more interested to see how he did on a better Rogue fight. Tidewalker, FLK, Al'ar, Solarian, etc.
As for Relentless Strikes vs. AR, it's pretty easy to find out which gives more energy. We'll say you're using a 1s/5r cycle. That takes 6 CPs. Two of those you have a 60% chance to get free, so we'll say you need 4.8 CPs. At 35 energy per CP, you need 168 energy, which is 8.4 seconds (we're speaking in averages, so I'm not going to round anything off). You've also got two 25 energy finishers, for another 2.5 seconds worth of energy. This means our cycle takes 10.9 seconds. We get a 20% chance for 25 energy, and a 100% chance for 25, for 30 energy returned per cycle. We'll say the boss fight lasts exactly 5.5 minutes, which is the best case scenario for AR/Prep. You'll get to use AR 3 times, which yields 450 energy.
Relentless strikes gives us 30 energy every 10.9 seconds, which in a 5.5 minute fight, is 908 energy. So, in pure energy generation, Relentless Strikes is over 100% better than AR + Prep. What about the DD factor? We'll say that AR + prep gets both the last ARs in under 35%. This means they get 300 energy during the best time to get the energy. 11/27/23 gets its energy spread evenly, so 35% of its 908 comes during this time. This comes out to 317.8.
I'd say that's pretty conclusive. The extra ARs in under 35% don't make a difference, and Relentless Strikes just plain beats AR + Prep.
My guess as to why he beat everyone on DPS is because of double Blade Flurry during AR, granting him a much better showing on the damage meters, while not really contributing a whole lot more.