from what i know, if 1 out of 4 cylinder break down(ie spark plug not working, or its cable or power), the car can still move, but lose like 50% power,
but 1 out of 3 cylinders break down, there is no chance it can still move

problem is no matter how much stuff or balancing shaft u add to ease the vibration
3 pot is still 3 pot, it's not balance
the balancing shaft only prevents the vibration from reaching the cabin/driver only
sooner or later, weird noises are going to come out

look at out viva, kenari, kelisa...the belting noise is infamous

noise that a normal 4 cylinder engine will never have

work as a foreman b4 for short amount of time(uncle's workshop), sometimes it doesnt really design's problem, like sometimes some ppl wash car, they wash engine, and they screw themselves up, sometimes ppl just itchy backside, DIY this and that, replace spark plug cable, replace spark plug. sometimes its hardware issue, like engine oil go into cylinder, spark plug distributor problem ... so it might not be design problem, low quality product also create problems.