Here's my take on modular bumpers. I think they are a neat concept but, in the long run they don't last. Every overlap or butt up connection is a breeding ground for rust to start due to the collection of water, road salts, brine, mag chloride and other road detritus. There have been several modular designs that the selling point is what you have in mind. Damage a wing.... unbolt it and slap another on. Problem is that a majority, if not every time, the connecting member is twisted or bent and it doesn't line up correctly, hits body panels and/or just looks like crap. Most throw them away and buy a conventional design from the guys I've talked to.
Pronghorn, MetalCloak, Rugged Ridge etc... I've never seen one that was capable of accepting a replacement component after a wreck or hard hit. The Pronghorn, no matter how tight you got the bolts, the components will still shift when bumped in the rocks. Even a slight shift damages the paint or powder enough to start the rusting phase once its exposed to moisture.
Strength wise, take a modular design and hit something; rock, dumpster, car, tree, etc... Then take that same modular design and make the shell one piece and repeat. I'll put my money on the one piece all day.
In the end its more about the aesthetics a customer wants from what I've seen. Just not my cup of tea.
J