That was flier vs. flier combat. Your suggestion of twoll heavies would be flier vs. non-flier.
We already know the rules for flier vs. non-flier, very explicitly, from the initial battle plan to take out the siege.
Point two is the important one:
In other words, Ansom (a flying 'stack' of one commander) could selectively engage Wanda (non-flier).Flying stacks with a commander may selectively engage non-fliers on their turn