Umm... No it doesn't. If you have too slow of a powder, not enough of it will burn while the bullet is in the bore, and the rest of it will be expended as muzzle flash. If you have too quick of a powder, it will all burn and all of the gasses that it heats will be fully expanded by the time the bullet is a quarter of the way down the barrel. The remaining portion of the barrel will slow the bullet down before the bullet even leaves the barrel.
To get a high velocity from a heavy bullet with a short barrel, you would need very hot, very quick burning powder, which seems to me to be Unique, at this point.
As proof for my first paragraph, try loading a .38 special with a short barrel with H4831, one of the slower burning rifle powders, and firing it. Next try some Bulleseye (after you make sure that the slug from your previous shot is not stuck in the bore). Try the maximum load of H4831, and try the max recommended load with Bulleseye. Which one actually clears the muzzle with some recognizable force? Which one falls out of the muzzle?
Next, try loading a 26 inch barreled .30-06 with H4831, try a starting load, then work up to the max, and then try it with Bulleseye. Load both to the same pressure inside the case, just so you don't blow your gun up. Which one clears the muzzle with enough force to be useful? Which one sticks in the bore, or barely clears the muzzle?
You can not make an oversimplified statement like that, and expect it to be always true. Sometimes quicker powders are better, sometimes slower powders are better.
Disclaimer: What you do with firearms and reloading equipment is your responsibility. Always check your loads against a published reloading handbook, and NEVER go above the published maximum load. Better yet, stay away form handloading, lead, primers, and powder; and all other things related to firearms, as discharging and cleaning firearms exposes you to compounds that are known to the state of California to cause cancer, birth defects, or other reproductive harm.
