I love it. You put forth how Mage Armor does nothing and Shield does everything, when I say that's not the normal experience you go out of the way to say how you have a normal experience and you specifically provide numbers.
Then when I use your numbers you backtrack on them as well. If you post numbers to prove your point, the next post saying you made them up - well, it doesn't support your point strongly.
+3 will have 3/5 of the effects of +5. Saying "15% is nothing and 25% is OMG EVERYTHING" doesn't hold water.
Combine that with one round vs. eight hours, so that +3 comes into play a lot more, and it will have more effect. +3 just twice is greater than +5 once over time. And you're already been clear that it's not the case you only get attacked once a day.