Battle of Hoth

So, I was watching Empire Strikes Back, I love the Snow Speeders versus the AT-AT's, one of my favorite scenes in a movie. As I was watching I thought this was a mismatch, snow speeders versus AT-AT's, man what a slaughter. I mean the Alliance fought AT-AT's with crappy radial cannons and guys with rifles. Why the frick didn't they have better cannons? Yes, I know they are the alliance and cant get their hands on the greatest weapons. But they did have the Ion cannon which disabled a star destroyer, can't we turn, pivot, move the Ion cannon to fire on the AT-AT's. Second thought-- would a win at Hoth have brought more systems into the Alliance earlier to fight the Empire?