I don’t get why they call it an Iron when they add apes and a headlight fairing though [emoji23] An Iron is supposed to be a basic, bare platform for you to mod.
As for the “underpowered” thing, everything is interchangeable with 1200 parts. If you really wanted to, you could find low mileage stock 1200 jugs from someone that went big bore for cheap and damn near double your power.
Besides actual power, I’m pretty sure the 883 has a shorter primary drive, so a 1200 converted 883 would feel more torquey than a standard 1200. Same idea behind people swapping XB9 primaries onto their XB12.