The point is that the one handed hammer and two handed hammer can CC crowds better than the shield can due to the nature of their attacks (one handed attacks really fast and basically bashes everything at hyperspeed whereas the two handed has huge AOE) and the one handed axe does way more damage.
So there's no real reason to use the shield as the shield is slower, does less damage, and CC's less than the hammers. Also has less dodge. Its only benefit is more stamina, which you don't need. After all, against bosses who can't instabreak all your stamina shields you can already block them forever with just a one handed weapon and with bosses that damage you through block or break your shields, you need to dodge.
I prefer to use the one handed axe because I can CC crowds with flamethrowers. So I don't need the hammers. Also I have an orange one handed axe so it's basically the only choice for me. Not to mention I like the axe's natural AP damage, which when combined with the ludicrious attack speed (my orange gives me a lot of AS%) just chumps enemies to paste. If I had an orange one handed hammer I would like to compare performance.
When I play Ironbreaker I'm usually top of every single score except for special kills. Most damage, most ranged kills, most melee kills, least amount damage taken, etc. There's no real reason to play any other class. I think IB is really easymode but I can't get enough of the flamethrowers. When I try to play anything else my performance is usually subpar, which speaks volumes to how strong IB is.
The DPS output from one handed weapons is unreal on him. You should just craft a random one handed axe or hammer on him and give it a shot before knocking it. It sounds stupid but it's really noticeable how much of a difference it makes.