If only this was true, comparing a 24 hunter to a 20 p2p and f2p 20; 24 > 20p2p > 20f2p.
You are not able to stack as much raw damage and crit on a p2p 20 compared to 24 even with scaled stats because gear is much better for a 24 which makes me wonder if the posters above even compared this in bg.
BoA's will all be the same, so let's look at offensive stats on off-pieces.
24:
WSG Necklace - 6 agil
Parachute Cloak - 8 agil
Emissary Cuffs of Agility - 9 agil
Foreman's Gloves or Ashen Gloves - 5 agil/5 expertise or 7 agil/4 crit
Satchel belt of the Bandit - 5 agil/5 crit
Standard Issue Prisoner Shoes - 8 agil
Charged Gear - 9 agil
Charged Gear - 9 agil
Glass Shooter - 12 agil/8 crit
71 agil, 13 crit, 5 expertise or 73 agil, 17 crit.
This is only hit capped if you're Draenei. Non-draenei can use the leather BoA shoulders (+2 agil, -6 crit), Ring of Precision (-3 agil), D-1000 Rng (-5 agil) or Dread Pirate Ring (-9 agil, +6 crit). If you use Ashen Gloves over Foreman's, you'll need 15 hit for your pet abilities to be capped. I guess this is optional since p2p hunters can pretty much faceroll through most things anyways. Rocket boots with surefooted are an option to get you there, you gain 10 hit/10 crit for 15 agil or 8 agil/minor speed, depending on your normal boot enchant.
20
WSG Necklace - 7 agil/2 stam
Parachute Cloak - 10 agil
Black Wolf Bracers - 4 agil/4 crit
Foreman's Gloves - 7 agil/7 expertise
Satchel Belt - 6 agil/6 crit
Feet of the Lynx - 10 agil
Argas Ring - 7 agil
Ring of Precision/Dread Pirate Ring/Ello's Band - 7 agil/6 crit/4 agil
Naga Heartpiercer - 16 agil
74 agil, 10 crit, 7 expertise. (67/16 or 73/10 with DPR or Ello's)
20 also has the option of using Cloaked Shoulderpads over the BoA shoulders to stack agility, 12 agil vs. 6 agil/6 crit.
I don't know about you, but looking at those numbers I'd say:
General balanced BiS set will be relatively even - 20 will probably have a bit more agility, 24 a bit more crit.