Because one, most Pokemon are strong is either physical or special, not both, and two, if you only train them in attack or special attack the one you train will be higher though I am guessing now by your reply that you don't EV train at all.
Seriously??? No offense dude, you are good, but some of your move choices suggest you haven't been doing this long, so expecting an easy win against tried and trained gym leaders is a bit naive. Good game nonetheless.
Thanks for your H&S gym challenge. Of course, I accept. Please VM me when you are on next to battle and read the rules of the league and my gym. Cheers.