Garp against Luffy is alot different he wasnt at his fullpower. When weakened Aokiji beat him he still nearly lost and needed the help of other pirates.

Marineford Garp oneshotted Marco who can tank attacks from Akainu and Kizaru. Whitebeard never bested him,he hit Akainu with a full power sneak attack then Akainu just gets up and carries on walking

Old Garp is yonko level

Garp might not be in his prime or final form, but he still was going to kill Suzuki in marineford.