How far is your commute everyday?

rsx is good enough for daily commute
can consider raider too for extra power

get big bike if you want to have fun
under 20k you can find used kawasaki z650 with abs, bigger than kapcai and not as heavy as d400.
still easy to squeeze through traffic also

if you dont care about abs can find old yamaha mt07, size similar to z650

If work horse, just get a kapcai. Your distances is not far away. Big cc useful if commute through highway.

do take note big bike doesn't have space for luggage like raincoat or helmet

kapcai at least have bakul

Anything is flickable with enough practice on clucth and throttle control
I personally find the d400 is very easy and fun to filter like a pelesit.
Not an advice, but i did watch those indian street racing vid for inspiration and reference.
Just specifically to cilok on a d400.

I daily my 800NK. Previously my dominar with 3 boxes.

It takes getting used to and you won't be as nimble as a smaller kapchai or scooter and you might not be able to squeeze into smaller gaps in traffic. I still prefer the security and stability of a big bike over a smaller bike.

A 650 isn't any heavier or bigger than a normal 250 maxi scoot, and many daily on them.

Give the z650 or the 700CLX a try. They are quite nimble and does quite well in traffic