How is it independent? If all their SP's suck, the opposing teams scores a lot more runs, thus the things that go into a measuring a park factor are affected. If you have an excellent staff, the opponent doesn't score as much and the park looks like a pitchers park.
PF = ((homeRS + homeRA)/(homeG)) / ((roadRS + roadRA)/(roadG))
It's total runs, not just your runs.
For example, let's go by averages. Let's assume a team (both pitching and hitting) scores the same amount at home as on the road.
Every game of the year, they lose 7-5. They give up 2 home runs, only get 1.
((1 + 2)/(81) / ((1 + 2)/(82)
=
(3/81)/(3/81)
= 1.0
The fact the teams pitching staff stinks has no correlation to the park factor, because (presumably) the same stink rotten pitching staff is increasing the road runs per game as well.
Now, if the team has an away pitching staff and a home pitching staff, that would throw things for a loop. I don't recall the rockies employing that method though
If all their SP's suck, the opposing teams scores a lot more runs, thus the things that go into a measuring a park factor are affected. If you have an excellent staff, the opponent doesn't score as much and the park looks like a pitchers park.
This is exactly what Park Factor is meant to work against. It's also part of the reason I think CBP has been labeled a hitters park (we've had great hitters, which generally lead the league in runs scored, playing there 81 games per year the past few years, and horrible pitching staffs, which creates the illusion that it's the park, and not the hitters and pitchers, scoring the runs).