It's possible things are different now, but as far as I know the only pet buff you can give yourself BEFORE you enter the arena is serpent's swiftness (10% haste), because it's 2 minutes long. All the other buffs are wiped off when you are teleported into the fight (this is so you can't get a power word: shield or bloodlust buff for the beginning of the fights). That said, you should be able to get serpent's swiftness before you enter the arena and still have enough time to buff yourself with something else you may be missing (either 5% crit or 3000 mastery) before the fight actually starts. Back when I did it, you could set up your stable to apply a lot of debuffs to him (ravager 4% physical damage, wind serpent 5% magical damage, tallstrider 12% armor reduction) but with the stampede nerfs that doesn't work any more, so in the same ilvl the fight is definitely harder.
As people have said, the real key to this fight is getting through phase 1 quickly and efficiently, and survival is probably better for that. Activate multiple adds at once, DOT them up, and make sure not to waste extra damage on them if they are about to charge. You can run through the orbs with deterrence and take no damage from them (twice with readiness), and have multiple ways to stop his heal. Aim to get through the first phase with at least 45-50 seconds left, once you do that you should have a kill soon. I also found that it was worthless to attack him when he first appears and walks to the middle because he healed up while shielded, but I heard from someone who killed him more recently that he doesn't heal up any more, which gives you a few extra seconds to get damage on him. That said, don't let that distract you from the really important aspect of the fight, which is handling the adds properly.
Oh, and if you activate an add and it gets stuck in the ground or wall or something and evades or vanishes, it sucks but there's nothing you can do. If you're sure you can't get a kill then dismiss pet and feign death to be ported out quickly so you can queue up again.
Here's a tip that anyone stuck on this fight might want to use.
Switching your trinkets just before the ahooro spawns. This starts a 45 sec cooldown and that should be enough to finish phase one (remember you won't have to attack the last 4-5 sec because the angel is charging). This helps to remove some of the randomness of trinkets.
I don't play a hunter myself (feral) but found this fight to be quite a hard dps check for my gear. I actually forgot to change trinkets at my kill (25th try?) but I got insanely lucky with procs in the last phase. All of my trinkets procced and I obliterated him. He died 7 sec pre enrage which is insane after all of the enrage wipes I had had.
This boss is amazing, just keep trying. My progression was quite bug free. The first phase does get a little brainless in the end and promotes charge-mistakes and such. Just keep cool and do a few breaks in between and you'll do much better in phase one.
Did it with around ilvl 525 or there around. Was really cloose, only had a few seconds spare. Its really alot of rng where the angels spawn. Good spawns can make a massive diffrence in how much time you have to burn him down.