Always change all together

bcos i rotate my tire regularly, until all worn out near the little 'pimple' in groove.
never bother about change front or back

Personally I'd rather have more grip in the front. Not being able to evade something that is in the way, or not being able to drive a corner and instead going straight (down a mountain, into a building, other cars...) sounds terrifying. Also, the front brakes do most of the work. If you have poor front tyres, stopping distance will be impaired. The only advantage of having the better tyres at the back is that it won't break loose so easily... but that can be brought under control by the driver... while for the disadvantages of having poor tyres in front there is _nothing_ you can do. You are going to crash, no matter what.

ESP also helps against rolling the car (especially important for taller cars... something like a Kancil, Viva, MyVi, Kenari, SUVs, pickups, MPVs, ...

I would also doubt that chances of loosing the rear is lower. I'd say it's exactly the opposite. You can easily control a Caterham during a drift... long wheelbase. A Clio V6 has to be driven by a master if you want to drive it at the limit... the rear will easily overtake you, and balancing it is hard. As soon as the rear breaks loose... Of course most small cars are not rear wheel drive, only the smart fortwo is amongst newer cars, and the Clio V6.

I just asked an engineer. He says short wheelbase is easier to spin

When taken to the extreme, the snap-oversteer in a short wheelbase can be scary (that was what your engineer was trying to explain) but that would be more on the fault of the driver than car. Most snap oversteers that I have seen were due to an over enthusiastic driver entering a corner way too fast and trying to brake too late into the corner and hence unloading the rear tyres.

Even if that is true, longer wheel base cars tend to have wider, grippier tyres.

Small car with wide tyre might be prone to hydroplane...