With few exceptions, the percentage of tower sitters is about the same on all sides. If this rule applied to all sides, the relative difference would remain close to the same, so functional ENY would be no different.
About the only time tower sitters are out of wack is when one side is close to winning the war. They either A) switch to the about-to-win side, mistakenly thinking they will get their perk point award, or B) stay logged in thinking they need to be logged in to get their perk points.
Yes, it's a mess, but it's what we gots, and the downsides are greater than the upsides when you step back from a myopic view of "I can't fly my D-Pony"