@upYOURS
Bro, under-powered is a relative, and not an absolute term (other fellows have explained very well).
I myself own Passo X, 2013 model, and it feels under-powered when; you are 05 adult passengers on-board, boot is full of luggage, AC is running at full and then you have to overtake! otherwise in normal conditions and especially in winters (when AC is turned OFF), it does not feel under-powered. Condition of car (engine, transmission, filters, cleaned catalytic converter, plugs, Tire pressure, etc.) also matter.
What can be expected from a 03 cylinder 1 KR-FE engine, which makes lot of noise and vibrations (due to being 03 cylinder)? and when the self weight of car (Vitz, Passo / Boon) is also huge! Noise and vibrations further increase when you have to overtake and push the pedal to it's max.
(If you have to do it, just turn the AC Off for a few seconds and then turn it ON again. No issues.)
Weight of vehicle to Engine Power (or Torque) ratio also matters.
Just compare 1.0 Vitz with 1.5 Vitz, things will be more clear.
Regarding 0-100, Passo takes more time than Vitz, and I think for this, shape / aerodynamics of Passo are to blame, otherwise, 1KR-FE engine and CVT transmission (which are the main things) are the same in both Vitz and Passo.
Passo is a decent and nice family car, good enough for day-to-day matters.
In severe hot temperature (42-43+), there is some decline in AC performance, otherwise for 9-10 months for the rest of the year, it works flawlessly and efficiently.
I think, that noise is due to being 03 cylinder engine. Ist generation 1.0 Vitz came with 04 cylinder engine, however, with 2nd generation and on-wards (till now), 1.0 Vitz comes with 03 cylinder engine. 1.3 Vitz is 04 cylinder since day 01, so no noise and vibrations issues in it.
Current generation Cultus (Celerio) also has 03 cylinder K10B (K-Next) Engine; vibrations and noise issues can also be there, but their owners can better comment.
Rest @usama1 has also rightly said. If you are about to spend 1.6 million PKR, then brand new, zero meter car can be a wise decision, but also consider following things:
I have Passo, and I never faced any major issues. JDM cars have exceptional and excellent build quality, and 5 Grade (or above) and 2015-2016 model year (or above), low milage car (be it Passo, Boon, or Vitz) can never be compared with a brand new, Zero meter Wagon R, Celerio, etc. Regular, routine maintenance cost is also comparable with that of PKDM cars. Yes, spare parts are quite expensive, but available in all major cities. These cars also do not break down that easily (Dhooka Nai Daitein!
)
PKDM / JDM both have their Pros and Cons, but ultimately, one's choice and money matters. As in here, your money, your choice!
I Hope, it helps too. Thank you.