I guess I don't see too much to complain about when it comes to teams whining about matching up against certain teams on certain shots.
As long as the league agrees to the oil pattern schedule BEFORE teams numbers are assigned and the schedule determined, it is all just luck.
As for days when the shot is different on some lanes due to equipment malfunction or something like that, once again, the league standings only reflect how you bowl against the competition on the same pair that night. The only time this issue comes into play is if there are brackets and side pots which are not the leagues responsibility. If the mechanic accidentally gave half the lanes a house shot instead of the U.S. Open pattern, then the bowlers are competing on fair conditions for that night since both teams bowl on the same pattern.
I personally would want more than 2 weeks on a particular shot before changing since it may take more than 2 weeks to get in a groove on the shot. A 4 (or similar) week interval seems like a good length of time since it would give the bowlers a chance to get used to a shot and perhaps get some good scores under their belt. This would improve moral of the league, improve the chances of slightly higher averages and increase the number of repeat bowlers the next time you have this league.
I am not a pro-bowler, but I do play one on BallReviews.com