Pheasants are a bit more tenacious than doves, or, grouse, or woodcock, or quail.
Agreed, based on my shoots of pen-raised pheasants, never hunted wild ones, which I would assume are only tougher to down. However, the driven pheasants in the UK are also pen-raised and released, and supposedly provide great sport.
Sir Joseph Nickerson, who wrote the excellent book
A Shooting Man's Creed, and killed more feathered game in his life than Lord Ripon, used 20s and 28s for many, many years. He stated in the book that 13/16 oz. shot is a gracious plenty. I will defer to his experience. Any man who surpassed Ripon's tally in their lifetimes has my attention when he speaks of guns and loads.