Whitebeard is a fool:
Assumption: Luffy and BB did not arrive: only WB and the Marines
Think about it, out of all his commanders (before ace was rescued), only two, Marco and Jozu, are capable (probably, dunno w/ Vista) of fighting on equal terms with the 3 coloured admirals. Let's just say these 2 are occupied in fighting 2 of the 3: Marco vs Kizaru and Jozu vs Kuzan. In addition, other commanders, including allies, will be facing the vice admirals of marines. Hence, Whitebeard is left alone to face Akainu, who stalled him significantly to death almost. Here, Garp and Sengoku are not taken into account yet, in addition to the Shichibukai. I think if, post-Akainu battle, WB fights with Mihawk, who is on equal power with Shanks, it would consume all of his shits or take too much time, or if he still manages to defeat Mihawk, Garp and Sengoku are still there to deliver the final blow. I mean, duh, he can't save Ace.