There will no effect on profit ratio. If your cost price decrease before Tax, you can add your profit as desire by you and wise versa. If you are paying GST on your purchases, you will collect GST by your customer, and after availing ITC of your purchases, you have to differencial Tax amount. Then how the question of profit or loss arises?
i agree with you rashmi ji but after gst applicable i dont think so any change on his profit only tax rate change and this rate change for everyone his business profit depends on his purchase or sale and exp.