Weak braking after installing 66BHP Street Pro pads on CB300F

I recently replaced my OEM pads with 66BHP Street Pro semi-ceramic pads. I expected at least similar or better braking than OEM, but the braking feels noticeably weaker.

Front is okay at normal speeds but feels risky at higher speeds. Rear braking is very weak — it barely slows the bike even around 40 km/h.

Mechanic told me to ride ~100 km for the pads to bed in. I've now done around 200 km (mostly short rides) and the rear brake is still very poor.

Has anyone used these pads on a CB300F? Is this normal bedding-in, or could there be an issue with the pads, disc, caliper, or installation?