You're mistaken
Old Garp wouldn't fight and take down Akainu in 2 moves
Wouldn't also fight kizaru and Kuzan
While being stabbed by many,
Wouldn't also go on dominate Yami Teach
Garp using haki =/= being better than Old
Oldbeard /Sickbeard >~ MF Sickbeard >~ MF Old Garp >~ current Old Garp
Because WB attack power was still of the charts. But it's no mistake Oda chose to make WB sneak attack Akainu and not overpowering him in a direct clash.
And it was WB after Ace died, at its most enraged and most powerful
In a direct 1 vs 1 without outside interference WB would have lost against Akainu. He couldn't sustain a top tier fight and winning.
Headcanon Healthy old WB > MF Garp > MF WB