Don't forget the 0% for basic groceries, at least we have that in Ontario.
The good thing about more slabs means more optimised and lower inflation. I think 4 (effectively 5 with the 0% basic goods) slabs is fine....not too many by any stretch and it was reached as a consensus by many experts from the states that make up India.
That (inflation) was a bad problem in Canada for many goods when they first introduced the GST.
I mean 99% of the "complexity" is the actual hardware + network used for GST system. Actual effective tax slabs make little impact on complexity....might as well go the extra mile to minimise inflation or even give an inflation "rebate" to many consumers which is what I suspect will happen.
It will time nicely with the rebound happening in Indian economy right now.