I always thought it would be a fun to run a statistical analysis using flipper gap as the independent variable and things like pinside ratings, average earnings, average ball time, etc as dependent variables, but precise flipper gaps for a lot of machines were surprisingly hard to find. Put 5 people in front of the same machine and ask to measure the actual gap and you get 5 different answers depending on how they line up their ruler. Extend that out to multiple copies of the same machine with different rubbers and variance in flipper angles and it gets even muddier.
1/16th of an inch really does make a difference but its not easy to eyeball. Some games have clearly larger gaps then others, but individual and community perception of the gaps on different machines changes depending on how that table plays. Given 2 machines with identical gaps, one that tends to STDM is going to be perceived wider even if the cause is poorly designed returns on successful shots or punishing rebounds on failed ones.
Whatever a player's skill level and wherever they are on the nudging spectrum from "pinball is a rodeo" to "all movement is cheating" nobody likes it when a ball drains SDTM. Casual players will move on to something else and even skilled ones would rather play something where they can push the limits of risk/reward rather than play defense against the machine avoiding sucker shots and shooting the same loop over and over, save whatever notoriously punishing machines they mastered to pick at tournaments.
Shrinking the gap and/or installing a center post are easy fixes. Good shot/return angles make for a better game for players who put in the time to learn the rules and shots but leaves a lot less tolerance for machines that aren't perfectly dialed in and still results in more casual players getting turned off before they learn enough about the table/rules to get hooked.