Why though. Garp going toe to toe with Roger was always common knowledge. Garp is the father of Dragon and grandfather of Luffy after all, one being the protagonist and most significant figure and the other one being close as the Revo leader. Plus, they were both young, so Roger's growth rate may or may not had been slightly better, similar to Luffy outgrowing Smoker (an extreme analogy, because prime Garp in fact was close to Roger).
Remember, old Garp was walking through Aokiji's fruit related powers and smacking him around, until Aokiji started to go into CqC against said old Garp after having his abdomen stabbed. Same old Garp said he is going to kill Sakazuki.
If we wanna compare feats, Sakazuki:
- Was stalled by Vista and Marco for a prolonged time while being bloodlusted
- Couldn't stop a heavily wounded/damaged and brain dead Kuma while spamming his attacks, unable to properly aim for Kuma's face
All trolling aside, great pirate > admiral.