No offense OP but you're just doing something wrong.

1) Idk why you'd take MNK over PGL. PGL seems like a much better choice to me because you increase your survivability. Not saying you can't do it on MNK, but you need to be able to avoid Sear with near 100% efficiency or you will just be a burden. Unless you can avoid Sear, stick to pgl.

2) If you insist on doing insane damage then learn mp management with fists. You should be weaving in and out between Sears, putting your weapon away between charges and between your assaults. Also make sure to time your second winds..you dont want to eat a prism+cure/cura because you lost some hp lol. Its your only heal so use it wisely, usually in situations where if you didnt use it you'd probably die from a sear/aoe/whatever. But if you can't avoid Sears second wind will just not help you...so practice that.