Bigger caliber more range. So more damage at longer distance. The Chinese and N.Koreans have also made 450 mm and 600 mm mbrls. And the Chinese copied the smerch and made weishi series of mrls rockets.I have a question, my did India buy smerch in the first place? We had MRBLs as long back as 1999s where we used them in Kargil(maybe that too was imported). 20 years down the line, why don't we have a scalable system which can be mass produced. I highly doubt, despite not having any idea about internal complications of such systems, that a system like pinaka be very difficult to build. What does smerch offer us, which pinaka doesn't?
Weishi rockets - Wikipedia
en.m.wikipedia.org
They have more than 10 different versions of this mrls and have more range than the smerch on top of that they have exported this to Pakistan,Turkey and lot more countries in the Muslim world and Africa.