It's not cope, he did. "Leaving in the dust" is an overstatement but he definitely got stronger. They weren't in their primes on GV. Compare the performance of old Whitebeard and old Garp.
Are you seriously telling me that Old Garp outperformed Old Whitebeard? Of course not, Whitebeard's performance was leagues better and in a significantly worse condition where he couldn't even use CoC lol. Garp went down to one ex-Admiral who was significantly holding back after a single cheapshot that wasn't even fatal.
An infinitely worse condition WB (no CoC, no CoO) went down after a Squard cheapshot, heart attack, Akainu donut cheapshot (which was significantly worse than Shiryu's stab), a Kizaru laser, losing half his actual head, and then getting jumped by BB's entire crew, plus a million cannon strikes, stabs and gunshots along the way.
GV doesn't change the fact that we saw old Garp's performance vs old WB and WB cleared, easily, whilst being ridiculously nerfed to boot. A man who was canonically <= Roger. A pre-prime performance on GV doesn't magically change that. Whitebeard and Roger, after GV, went onto become the top 2.
People are being dishonest — no chance you seriously think that, if you drop a perfectly healthy old Whitebeard into Old Garp's shoes, that he loses in the same way or worse. Absolutely no chance.