Why you think that VSC only controls over steer? someone who drives a RWD can correct that over steer just as easy as you say someone in FWD will control understeer.
VSC is a full on stability protocol, it can be more effective in cars with more hp but it doesnot mean its not useful in low power cars. New city has a high road clearance which makes it inherently unstable, VSC uses sensors to predict the cars motion and inertia, it can then cut power or apply individual brakes or increase throttle to adjust it.
It is plain wrong to say that some cars dont need VSC, ALL CARS MUST HAVE VSC(ESP or ESC).
I think you are confusing TC with VSC, TC is just one part of VSC and the most basic of TC which you keep mentioning is the one which can be just achieved with an ABS motor and rotation sensor.
Altis is old shape but so is the city 6th gen, and thats it, altis is an upper category to city. If you want to cancel your altis and go with city 1.5 its your choice, in any case you will be getting an outdated model.
CIty 7th gen is priced equal to yaris worldwide, if anything the 6th gen pkdm city should be priced lower than yaris. But we know that aint gonna happen,
