Another two merits would push the modifier from 60% to 100% which is a substantial increase.

Using an fTP-boosting gorget and belt would increase the fTP from 0.6875 per hit to 0.8875 per hit which is a very substantial increase compared to the usual bonus for such gorgets and belts.

Without those changes, you're using a weaponskill with a horrible fTP value, a mild attack penalty, a pretty decent DEX modifier, and an inability to critical that makes the DEX modifier feel depressing. I'd expect the sad results you're reporting from such a weaponskill.

Your best bet is going to be culling two of your merit weaponskills and, depending on which remain, possibly obtaining the proper gorget(s) and belt(s) for them.

This isn't to say I think all of the merit weaponskills are just peachy keen in every way, but someone's equipment and merit set-up are far more likely to change than the Development Bros' concept of balance.