Need tips for Boss killing second skill :S

Hi everyone :).

So I've come back to POE after quite a few years and for the bestiary league I've chosen this build:
https://www.pathofexile.com/forum/view-thread/2063802/page/1

But As the build states it has problems with boss killing (t14+, red shaper, etc), as such I tried to get a good secondary skill that also goes well with the talent tree, but heavy strike seems lack luster :S.

So could anyone give me some tips?

My tree:
https://www.pathofexile.com/passive-skill-tree/AAAABAQBAAHnBLMFLQU8BWYHdQmWC2EMcA48E0wUTRRxFewX4RiRG_ohVSPTJd8m-CcgJ58ppSo4LPswdzWSOQ46Uju2PC1AoEMxRrdHfkh4TP9OKk4yUEdXVFn-WhpeE2EhYVJkUmWnaGVo8m8ncql07XTxdqx4enrve3R82YNfg8yE2YTvhVKFp4ZghrSHaooiirOK8I9gk6iXeZpqogCkGaU1qSeplK2NrlCvbLKAtz65HbyfvTbAZsCmwaPDM8T2xVPGrsqQz37Tb9i92WHZfNrB3DLcPeCf4mHkUelG6hjrCe8O707wH_Pd9WH3Mvjr_Ev-Cv6P?accountName=ezakhiel&characterName=Shunpoo

My current gear and offhand weapon: