I played with "buckshot" a bit in a CYL bored 12 gauge and a Bess. I put "buckshot" in parentheses because I was using cast 32 and 36 cal balls rather than hardened commercial buckshot. I've also used a lot of modern buckshot ammo for called coyotes rather than deer.
Basically, they're really different beasts. With chokes, buffers, hardened shot and load testing, I have been pleasantly surprised with how far away we've been able to hit the yodel dogs. But that's different than deer. We were willing to accept wounded coyotes, so long as they just got the hell away from our place. But in fact they were pretty easy to stop or kill outright with single hits. To assure lethal hits on deer, I'd want a lot more hits and have to shoot a lot closer to get them.
I could probably improve on the range I was getting with the MLs through load development, but probably not by all that much. Using an arbitrary number like three hits to assure kills on deer, I'd have to say my loads and guns couldn't be depended on past 20 yards or so. If careful loading and choice of components stretched that to 25 yards I wouldn't be too surprised, but I sincerely doubt I could push it past 30 yards. Long as a guy respected the limits of the loads, I don't think he' have any problems.
At one time there were places that required buckshot for deer, so switching to a single ball wouldn't be an answer. But I'd sure prefer to use the single ball rather than rely on buckshot.