In most Pokemon games, stats are everything. Two Pokemon born and raised identically can have radically different battle styles and perform very differently, as their stats change over time. While this is true to an extent in Pokemon Go, the system is much simpler, boiling down to moves and elemental weaknesses, as well as CP, or combat points, the end-all-be-all measure of Pokemon strength. It may be unthinkable that, say, a Weedle with 15 CP can actually take down a Pidgeotto with 1,500 CP, but it's entirely possible, if a bit painstaking. Basically, this is because the gym battles happen in real time and there is a dodge mechanic in place that actually does work, so long as your connection is fast and stable. As anybody who plays games like Dark Souls or Monster Hunter will tell you, if you can dodge it, you can beat it, even if it's multiple times your size and could likely knock you into next week with a single casual attack.
While catching powerful Pokemon and training your own Pokemon to be powerhouses will win you battles, that's just the mainstream method. Hardcore gamers with split-second reflexes and twitchy fingers may be wondering exactly why they're so addicted to this very casual game, but there is something here for them after all. When you're in a fight, a swipe to the left or right will make your Pokemon dodge, while a tap on your Pokemon will make them attack. When an enemy Pokemon is about to attack, a yellow flash will give you about a half-second's worth of warning. A quick dodge will spare your Pokemon a punch, fang, or Hyper Beam to the face, and you can follow it up with a quick attack or two. Then, dodge again, rinse and repeat. Since the dodge mechanic clears all damage regardless of level or element, using this correctly will literally guarantee wins.
The tactic boils down to two key points, both of which almost any action gamer familiar with prevailing against bad odds will tell you. Rule number one, never lose focus. A single missed dodge may not always spell loss, but it can knock you out of your flow and leave you sloppy for the rest of the battle. Rule number two, never get greedy. If the power difference is so drastic that you're thinking it may take a few hundred hits to finish the enemy off, well, it might; but don't let that discourage you, or goad you into thinking you can get in more hits than you actually can. Start with one attack per cycle and count the tenths of a second as closely as possible until the next attack. If you can attack more and you know that for a fact, go for it; otherwise, abstain. If you're vigilant, the enemy will fall eventually. If you slip up, your arrogance will cost you the battle.