As long as your pheromone kiters don't drive Garalon like Asian women, you should be okay to move between the leg zones to help cleave down the legs. In our 10M, we have pretty much the entire group moving from leg to leg. (Though we tend to ignore the ones which spawn on his far side, allowing the melee to handle those.) You're missing out on a good chunk of raid DPS if you keep to much of your raid outside of the Weak Points buff.
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We kill all the legs at the start and after that the tanks and our only melee DPS kill the legs as soon as they respawn.
I think your damage looks fine. In comparison it looks like the rest of your raid needs to up their game. Going into Garalon with only 1 melee makes things harder but is do-able, I do not have any logs that show a kill with 1 melee but here is our last kill of Garalon:
The fight is a lot different with only 1 melee, so take everything with a hint of salt.
Our damage is pretty similar. I was pheramone kiting and was not dpsing the legs as both melee covered it. If we were to ever roll with 1 melee, we would always have 1 person assigned as simply multidot, if the melee needs help he'll call for single target nuke. an important thing to note for progression is nuking a leg within 10 seconds is an overall dps loss for the raid. Keep the leg up as long as possible and if it dies as close as possible to the next one spawning, all the dps done was efficient. Due to the change to cleave mechanics, it's not as important anymore however.
I can only notice that your devouring plague is a lot lower than mine. I am taking DI over ToF since I am not damaging legs so the comparison isn't 100% fair as I will be doing more DPs than you. Just make sure you have your trinkets + CD's popped with as many DP's as possible, I will always delay my DP pop if Mind Blast is still on cd and a trinket is <4-5s from coming up. There is no wasted DPS from not DPing immediately as long as you never delay a mind blast cast. Managing DP correctly gains you massive DPS increases as spriest.
I think the best way to make progress on this fight is to find a strat that works for your guild. We find it best to roll with a kiting rotation of 1 healer - 1 dps - 1 healer - 1 dps and we 3 heal the fight. It boosted our raid damage output hugely whilst maintaining stability. At about 25% we let the last kiter hand it over to tanks, then execute. You'll hit enrage before the pungency debuff becomes unhealable.
So basically, you are doing a fine job. Your fire mage is not. With a correct strat and with the low dps'ers upping their game you should have a kill. I don't think anything less than 50kdps is acceptable even for a kiter.
Try to have DP ready to cast on the legs once you get in the circle. Don't hold 3 orbs forever, but watch the mend leg timer. If one is about up, save DP a few seconds longer. Never miss your sw: deaths on them, either. They're huge. Make sure you're keeping dots up on his body the entire fight, too.