Actually not true, While they do have less aid due to sexism that doesn’t tell the whole story, First Pegs are also generally faster so they lose less speed on rescue as such have better surviveabilty not getting doubled as much,
Second CON they have less as such they have equal or MORE AID anyway,
Here is each GBA Game with the Aid Calcs and a light analysis of the Wyverns performance as Rescuers in comparison.
In FE6
Shanna = 16 Aid peg 15 Aid Falco
Thea = 15 Aid peg 14 Aid Falco
Juno = 13 Aid Falco
Miledy = 10 Aid WR 9 Aid WL
Zeiss = 15 Aid WR 14 Aid WL
Firstly you get both Shanna and Thea very early as such they get full credit for all the flyer rescuing pre Milady and Zeiss’s join.
Overall Pegs out pace Milady and keep up/out pace Zeiss, he joins late unpromoted at the start of the late game/end of mid game, as such while still good is fighting with others for deployment and whips and doesn’t want to be rescuing as he needs exp to reach promo level and keep up with Milady Percival, and other trained units.
He also once promoted is only on par with promoted Thea and would rather do combat with his high strength and good enough speed, it’s not good enough to avoid doubles attacks if rescuing unlike a trained Shanna.
Although Zeiss out performs Juno… almost everyone out performs Juno…
Verdict
Pegs superior rescuers/ utility due to lacking Wyverns and higher or equal Aid.
Also your Wyverns do combat, Pegs can do rescue while your Wyverns do combat.
In FE7
Florina = 16 Aid peg 15 Aid Falco
Fiora = 15 Aid peg 14 Aid Falco
Farina = 15 Aid peg 14 Aid Falco
Heath = 16 Aid WR 15 Aid WL
Vaida = 8 Aid WL
We will Ignore Vaida her rescue is dog water
Interestingly in FE7 Heath is just Zeiss but really good at rescue, he does need a few levels to promote but joins early enough that he’s not really fighting over promotion, he also gets HMBs.
Heath is a really good combat unit if trained and has the same con as Florina letting him rescue promoted Hector even if he is promoted, allowing him to fufill a rescue utility role if untrained, although every peg can do this and if untrained [Only if unpromoted for Farina and Flora], Farina is still better in untrained since she has better bases.
Verdict
Heath is really good at rescue and combat probably the second best rescue [of the fliers] in the game, although there are probably better things you could do with him then ferry Hector [or whoever] all over the place, and Florina does it for longer and doesn’t have any major combat you want her doing. Combat that Heath would rather be doing. but he’s still good and you can have him fly in with someone to do combat together.
FE8
Vanessa = 15 Aid peg 14 Aid Falco 11 Aid WK
Tana = 15 Aid peg 14 Aid Falco 11 Aid WK
Syrene = 13 Aid Falco
Cormag = 14 Aid WR/WK 13 Aid WL
I think this is pretty easy Peg → falco is the best Aid out matches Cormag by one
Although Vanessa does prefer WK for pierce and combat usually becoming a good combat unit, same for everyone else, this leaves Cormag and Syrene as the best rescuer if you do so however Vanessa is generally a peg for a bit untill the first whip shows up in Ch 8, doing most of the rescue for the game, regardless Falco/Peg are still superior for rescuing.
Though usually you aren’t rescuing super high con units as much in FE8 as they tend to kinda suck, good units like Epharim has 8 CON in lord and 10 in Great Lord and Seth has 11 CON allowing any mount to rescue them.
Verdict
The META of Sacred Stones does lead to units going WK though this is not for the need of Rescue it is for better combat. The fact the best units have low enough con to be rescued anyway means that rescue is simply less useful, peg/Falco are still superior for rescue due to the higher aid gained from low CON.
In Closing
Overall Pegs are better at rescue and you get fewer Wyverns and you probably don’t want to waste them doing support jobs when they could delete the map, that combined with the generally lower Aid means that they tend to be worse rescuers, that’s not to say they’re bad, hell some are really good, there are even situations you want them to rescue [such as in Chains or rescuing a partner into an area to delete enemies together], but it’s not the thing you are going to do with them most often.
Pegs on the other hand do have the room to play a support role as they tend to be worse at combat doing clean up or reaching side objectives as they lack the combat prowess of Wyverns, they are also more common and join earlier allowing them to do things Wyverns just can’t, they can get early resources if needed and generally will be at least somewhat trained.