the heavy head means that you don't need to put so much energy into splitting a small log. It's not a case of needing to use a maul for small logs, it's just more efficient than a small axe IMO
taking my own firewood example. I tend to split enough wood to almost half fill my 2x10x6 foot wood store each time I top up, so a fair number of logs.
I started out using a full on maul which is normally used 2-handed, but with the small logs I split it is overkill and I spend a lot of energy walking to the end of the handle (to use 2 hands) and then bending over to pick the log up. The weight is enough to easily split a large knotty log with power, but the birch doesn't require much more than a drop of the head.
If I use a hatchet, then I avoid the walking and bending and I only have to think about picking the log from the wheel barrow and then swinging the axe in the other hand (then I crawl about putting bits back into the wheel barrow to be split further, thus only bending once or twice per barrow load). Because the hatchet is light (1lb - 1 1/2lb) it require me to use force to get it through a full log, so I end up swinging hard and often not getting teh axe through the log on the first attempt.
The short handled maul is heavier to lift, but as with the other maul requires little force to push it through the log due to its weight and geometry. The bonus is the less walking and bending just like the hatchet. The best of both worlds, should a log require more effort than a simple swing (as you would on kindling with a hatchet), then I can give it some and be confident that it will go. The short handle means it is no more unwieldy than a hatchet, assuming that you can lift it easily in one hand (also the maul has a shorter distance between edge and handle than some hatchets, this makes it much easier to get a good angle on the log and is easier on the wrist as you don't get that twist)
I think it needs to be tried to see what works for you, but for me it is ideal for splitting small logs. I wouldn't split kindling with it mostly because I would spend a lot of time running across the room/woods collecting little bits of wood that have been throw aside

In the case of kindling I agree the heavy head is a disadvantage.