Yamaha always had low end torque but lacking top end. Thats why not so much kw's but very reliable compared to for example ktm's. It might not be fast as ktm 690 at higher rpm's but should pull ahead in drag race as ive seen in videos.
It has more than enough to pull away from cars in traffic

I compared it to KTM 690 cause I compared xt660r vs 690r before I bought xt660z.
Also check youtube videos, theres plenty of xt660 acceleration videos and hill race vs ktm