I don't know if I'd call 100% handicap leagues fair. Usually, lower-average bowlers find it much easier to improve over the course of the season--at the end of the league, most of the 115 bowlers end up as 130 bowlers, but they're still handicapped as though they're 120 bowlers.
I was in a league two years ago that was scratch with a max team average of 830. Not that it's foolproof, but that's one way to blend scratch and handicap formats.
I bowled in a mens league for a couple of seasons that was 100% of team difference. It also used a 7 point system, 1 point per a game scratch and handicap and 1 for total. Both years the top average teams were near the top. The second year the high average team won both halves to win the league outright. As long as there is no sandbagging the high average team is always at an advantage. They are more likely to hit average on a consistent basis. It's true the low average bowlers have more room to improve but the higher average bowlers are more likely to make their average on a consistent basis.