[quote=@Dynamo Frokane]
Could you maybe handwave the ammo we use as being smaller and weighing less, which allows us fighter jets to have more ammo but just not a high as rate of fire or damage as the mechs?

Not trying to change continuity here!
[/quote]

Don't worry about changing continuity here, I'm totally open to ideas and changing things. Let's see... perhaps we can say that aircraft guns are smaller and higher velocity, allowing more to be carried, compared to more stopping power on mecha. How does that sound? Let's say that triples the amount a plane can carry.