There's no doubt that the .30-06 is a superior cartridge as compared to the .303.
However, there's also no doubt that the .303 is a VERY effective round in its own right.
Canadian Industries Limited (CIL) made extremely good hunting ammunition for the .303 British, and I managed to chronograph some of it back in the 1970s. CIL claimed 2540fps for the 180-grain load, and my chronograph said that the stuff actually did develop that speed! I have chronographed a few .30-06/180 factory loads that did NOT make that much velocity.
A hundred feet per second plus or minus is essentially meaningless, but I can assure everyone, from PERSONAL experience, that the .303 British is a deadly round on moose, bear or whatever, and every bit as good as the .30-06 (for which I also have a deep and enduring affection).
Rimmed cartridges are a natural fit for classic single-shots, and the .303 and I go back a long way together. I also believe I saved my life with a .303, which tends to affect one's view of the round. Anyway, I have already placed my order for one of the new Ruger .303s, and eagerly await its arrival.