On their first encounter he could, in the second fight Whitebeard would've killed him.
After the blow from their second encounter, WB was killed by some rookies and criminals with basic weapons and casual attacks.
After the blow from their second encounter, Akainu went on to fight all but two of WB's commanders and dozens of their allies, all seasoned and experienced New World fighters, a few which clashed with Admirals and Yonko-level fighters. And he left that fight without another injury.
So, and just for complete clarity, you're telling me that Akainu is inferior to Teach's rookies and cronies and their basic attacks, as they did what you're saying Akainu would fail at doing, i.e., kill WB in the timespan following the blow that blew out the ground in that second encounter? You're telling me Teach and his measly, ragtag crew at MF, could kill all but two of WB's commanders and dozens of seasoned pirates using basic, freeform attacks?