Question about newborn weight

Our LO is 3 weeks old born full term at 38 weeks .. He was born 7lb 3.6 oz then he lost more weight than the 10% limit i guess (i dont remember the exact weight he reached). He is exclusively breastfed and in terms of gain rate he has been doing fine (as per the pediatrician) gaining more than an ounce each day. My wife still feel that he is small compared to other babies and every ped visit she brings up the question "do i need to switch to formula?" and the ped keep saying that his weight gain rate is great. Currently he is 8lb 3.5oz and 20.5" .. Can anyone share their thoughts so I can comfort my wife she has been frustrated about how people keep saying that our LO is tiny .. Appreciating your comments, thanks.