I don't believe you can fix league bowling.
First society has changed.
The amount of entertainment available, quick gratification, me first attitude, everything is about money, the way jobs are structured, etc, etc, all conspire against bowling in a weekly set time league environment.
Secondly bowling has changed.
Many leagues had little prize funds with only trophies for 1st, 2nd and 3rd place and trophies for high games and series.
With the increase in scoring you have generated the haves and have nots.
Looking at men's leagues only.
40 years ago the averages in a mens league would be 140 to 200. Most of the bowlers would average 160 to 180.
With 75% handicap, which was common at the time, most bowlers were giving up 5 pins or less and at most 15 pins. Even with 5 man teams you were seldom spotting more than 50 pins.
Any bowlers felt that with an extra mark they could catch and beat anyone in the league.
Today the averages vary from 140 to 230. Most seem to be groups in the 180 range. With 80% handicap they are giving up 10 pins, if you average 140 you are giving up nearly 20 pins to the high average bowlers. They no longer feel they have a chance most nights with spots of 100 pins of more, that is a lot of marks to make up.
Also the better bowlers would move towards limited handicap/scratch leagues. You didn't see stacked teams in handicap leagues.
Plus virtually all leagues were 5 person. A high average individual or two on a team didn't throw it out of whack as much as they do in 3 and 4 person leagues.