You can do it. One can do it. A lot of people have done it.

Which doesn't mean if you're buying a bike to eventually do a century on I'd recommend flat bars to you. But that depends on why you don't like brifters and drop bars. (And why you like the bikes you mentioned if you don't like their brifters or drop bars.)

The idea of riding 100 miles without being able to switch up hand positions makes my shoulders hurt just thinking about it.