Lakainu was an active Admiral who can summon Buster Call Fleet and call for more help whenever he wants. Aokiji was a former Admiral, and he can't do that. That's the ''simple'' difference. WB retreated vs. random Marines for that reason as well, there is no point for fighting Marines if there is nothing to gain. You trolls simply want BB to fight Lakainu on a random island for nothing lmao.
Nope, BB wanted to sink the island since it was Marineford, vs. Lakainu there was no point on fighting and nothing to gain, he did what WB did before random pirates.