Well, I don't know that much about mauls.
For me a maul is that weapon used by that guy in Conan The Barbarian that severly damaged the columns in the movie when Conan fought those two muscle men who worked for Thulsa Doom.
And is also featured weapon on the cover of Warhammer FRPG second edition.
That Conan weapon is just made up. The problem with a superheavy weapon like that is that it isn't actually very threatening in battle because you're unable to swing it with any kind of lethal force. It's a problem with the limits of human strength (which comes down to the way our bones and muscles are made) and basic physical principles of force and leverage.
I saw a Youtube video one time of a guy (fairly big) who forged a "buster sword" like Cloud had in Final Fantasy VII. Cloud's advantage is that he exists in a fictional world of animated houses that are wandering monsters and other things that are totally impossible. He makes the lack of real world physics work for him. We don't have that ability! In the video, the guy tries to use the "buster sword" to chop up a wooden pallet. He is barely able to damage it and practically gives himself a heart attack. You just can't get any leverage with it... you're basically just dropping a metal bar on what you're attacking. Whereas if you had a modest wood axe you could tear a pallet like that apart.
Likewise, fantasy art shows "warhammers" that are like Thor's hammer. A Thor hammer used basically by anybody who isn't Thor is not very scary. You won't be able to swing it hard enough to do that much damage (at least compared to other weapons), and it will be really slow and will tire your arm out almost immediately. You'll probably never even land a hit with it. I would be much more scared of this:
It would especially suck to get spiked with that thing. But there are even better weapons than that thing, which is basically a medieval can-opener, if you are fighting somebody who is unarmored. Like a combat knife.
The real medieval maul was like a sledgehammer. It probably had about a 4-foot haft. It was good for the Hundred Years' War because the English longbowman was mainly interested in defeated the French armored knight. The longbow was great for that because it killed the knight's horse. The maul (along with the war hammer or "falcon beak") was a good back up weapon because you could go open up a French knight with it. Good luck trying to hit him with a sword... he was too well-armored!
It's all about the right tool for the job. If I'm unarmored, I'm not that scared of a guy with a sledgehammer. After all, he is slow to swing it and I can probably get away (he has to lug around a sledgehammer). What I'm really scared of if I'm unarmored is something like this:
That is a seven inch blade that says "bad mother..." all over it. It weighs a mere 1 pound
and will ruin you. I'd way rather see a guy come at me with a sledgehammer than with a KA-BAR.
If I'm in a suit of late medieval plate armor, I don't have to worry too much about the knife if I'm at least somewhat mobile. If somebody wants to take down my cheaty plate armor ploy, they will need something that will either take it apart (the war hammer), or just batter the heck out of me (the maul). In which case I probably give up so my peeps can pay my ransom... and if they don't then I still get treated like a nobleman by the other side while I lounge around under house arrest.
Most weapons are designed with a certain purpose in mind. They work best when used for that purpose. Some weapons, like the "Conan maul", never existed because they would not have been good at any purpose to which they would have been put. However, there were some limited uses of sledgehammers because of what was going on with the circumstances of the HYW and such.
