That's like saying Smoker earned himself as current Luffy level because he could beat him preskip. Garp's 38years old ago portrayal(which was faked out by world government to boot) meant nothing compared to prime Whitebeard/Roger. In his prime, Roger was viewing Garp nothing different from Sengoku when he was thinking he could die in a confrontation with Whitebeard. Even old and sick Whitebeard was considering stronger than Garp by Garp's long time partner(Sengoku)
Their portrayal as one of the two factions you need to surpass to become pirate king says otherwise
Marco's portrayal as the final rampart in Teach becoming the pirate king is superior to any other YC1s, his portrayal as Whitebeard's right hand, when Vista can match one of Shanks' top3 prove otherwise, his match-up with Weevil, who you rank as low top tier will prove otherwise