Well that depends on your reward/risk and how tight your stop is. A very tight stop and a reward to risk of 4 to 1 or 5 to 1, 30% can make you some nice money.
If I was WRONG 30% of the time picking tops or bottoms, I'd quit. It's like saying indicators don't work. Everything works. TA has zillions of tools and few traders with mastery of a wee tiny selection of them. To get a top is the same as catching a bottom. If you can catch bottoms, you have part of the key to catching tops. To be really successful I'd suggest 3 tools. First, some kind of framework that shows a clear mathematical relationship between tops and bottoms. Second, an excellent knowledge of PA - that alone will get you entries at max reversals. 3 As good a knowledge of how to make indicators work as the first two. But really, if you lack the first or third, PA tells you enough. Structure just gets you in earlier and tells you the move is complete so hang in for a big move. Indicators assist in fine tuning. Remember: conventional wisdom is herd opinion - it confines your development and guarantees abysmal performance.