A genuine 58bhp is going to need at least some pipes (maybe modded Honda ones), airbox mods and a '21 flywheel along with a decent setup. Tyga only got 58.5 without the card (see here, the dyno chart for the standard one (the blue trace here) agrees totally with what you say, revs to 10,000 or so then (just as a modded one starts to really go) it fades away.

Mine (Tyga pipes, HRC smartcard, open airbox, HRC jetkit) made 57 with a nice safe setup, 60.7 on the day then probably 63 or so jetted nearer (too near ) the edge.

The power you've got sounds about right and you want to be checking the jetting before you mod it any further (i.e. don't just drill holes in the airbox), the power of the standard one is just flat wrong, it's either a complete lie or not a standard bike.
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