#1 - You need to do a little more homework Every 4 is not quite the rule. Check out the centuries divisible by 400. :-)

#2 - You are having a limit crisis!! Congratulations. This is how many great thinkers came to be great thinkers. "What if..." "But what about..." "Why ..."

Limit:

Take 4 years (not including a century). Average is 365.25

Take 5 years, with leap year #4. Average is 365.2

Take 6 years, with leap year #4. Average is 365.16666...

Continue this process and see how you feel about 365.25 (just ignore the 400 problem for now.)