In terms of power, Akainu and Teach counter Luffy in a different way.
Akainu in terms of raw destructive force. Teach in terms of raw potentials of all his DFs.
Also, Gura-Gura can destroy plenty as we have seen in MF, but it does not reduce things to nonexistence completely like Magu-Magu does. Case in point: everything Gura-Gura hits still exist in some ways, in pieces or otherwise. Everything Magu-Magu hits does not exist anymore.
also in terms of revenge and retaliation for ace oda has an interesting approach towards revenge
Ace wanted to avenge thatch and was defeated by teach
Law wanted to avenge corazon and was defeated by doffy
Carrot wanted to avenge pedro and was defeated by pedorin
Scabards wanted to avenge oden and kaidou absolutely wiped them
Marco and the fam wanted to avenge whitebeard and again teach crushed them
If revenge is the basis of attacking someone and not a progression reason then you are damned in one piece verse so if luffy is going to face akainu eventually i think a much more solid reason is mandatory