You are right that the typical bikepacking handlebar bag isn't ideal for drop bars, but people use them just stuffed less full so they sit between the drops.
Yes I often see bikepackers with pretty large front rolls containing sleeping bags or tents etc and using them with drop bars would require some rethinking of that normal practice to make the roll fit inside the drops.
I would have said the same thing about wearing backpacks on tour a few years ago, but I am totally comfortable with them now. I keep the heavy items on my bike including water and tools. Usually my pack contains food and gets lighter everyday on tour. Since I ride where things are rough I rarely sit for hours at a time which eliminates back/saddle issues and hike-a-bike is a normal part of my day and wearing a backpack makes the bike easier to push and carry.
My experiences of riding with a backpack as a teenager definitely prejudice me against them. But that was before the harnesses got so much better. I do carry a small silnylon back pack as extra carrying capacity and for days off the bike, but my setup was designed to avoid a backpack and if I need to carry extra stuff my first inclination is to strap it to the saddlebag or stuff it inside under the "longflap"
I was once tempted to see if I could get a traditional saddlebag made out of modern materials as I bet you could easily save a pound. But for now the Carradice Camper works amazingly well. It's easy to get at stuff with its side pockets and wide drawcord opening to the main compartment. the Ortlieb handlebar bag isn't perfect as the lid can be a pain to close and the strap attachment is a bit fiddly, but it's quite light and sturdy, carries all my necessary stuff, when the soulder strap is on it's easy to carry around and the Klickfix mounting is very convenient and it's perfect for drop handlebars.
Having just two bags makes it easy to deal with travel off the bike too, which is a consideration for many road tourers, probably not as much for the bikepackers. I can pack the bike up and take my bags on most modes of transportation as hand luggage. And finally there's cost; the Caradice Camper is $85 and the Ortlieb Classic costs around $95.....and you could easily use a far less expensive front bag. The bikepacking bags are still a bit expensive if you get them from the small shops.
What I like most about these softbags is not so much the lightweight [which is nice] it's that I can ride my mountain bike as if it was a mountain bike on rough terrain without having to think about breaking a rack or damaging a pannier mount. That puts a big smile on my face.
I like not having racks for the same reasons. Even with 25mm tires I don't worry too much about reasonable off road stuff (as long as it's dry) as I know I'm not going to break a rack or get hung up on vegetation and it's easy to get out of the saddle on steep stuff. Also if there's something to climb over or cross I can shoulder the bike and carry it. I had to do that a few times on the Erie bike path to get over fallen trees and through some parts that were under construction.