A 4,000 hour pilot speaking here.
Air density is significantly altered by changes in altitude and temperature. Increases in both altitude and temperature reduce the density of the air (make the air thinner).
Resistance to air drag increases as the square of the airspeed. Thus, air density (or lack of it, because of altitude) has a much greater affect on balls that are initially traveling at high speeds than at slow speeds. Golf balls leave the club-face at 100+ mph. I don't know the initial airspeed of a 400 foot home run, but it is way faster than a basketball.
A basketball shot from the 3 pt arc does not travel very fast. Therefore the drag on the basketball from air-resistance is minimal when compared to a golf ball or a baseball. Assuming the same amount of initial thrust, a basketball WILL go further in the thinner air of Denver than at sea-level; but the difference is very small -- because the speed is slow.
Even the most fit basketball players will tire from oxygen deficit more quickly at 5000 feet than at lower altitudes. So, stamina IS a significant factor; and the athletes WILL need a few more minutes of rest in all games. Thus -- bench strength will play a larger role in Denver than at lower altitudes.
I hope Geno will be giving a lot of practice minutes to Banks and Stokes between now and the Denver games --- because they will be needed for more minutes.
Don't expect to see many players in Denver going for 40 minutes.