First there is no such things of weight class fighters in any airforce. What actually it is high/low mix fighters. Like f15 and f16. F16 was developed as low cost fighter not as lighter weight fighter. But low cost forced it to light weight.
Agian mki maintanance cost is not too much than Rafale. Neither Rafale's purchasing nor maintanance is cheap, while maintanance time is where they provide profit. The advantage of Rafale of 3 flights per day is something we can not achieve before a decade due to budget restrictions.
Third Rafale's purchasing kiling thrice of the fighter projects of India.......lca, fgfa, amca.
Forth timing of Rafale is most valid point of its induction. The first squadron will be operational by 2018. Although surely they provide benefits compare to mki and lca and even over super mki. But if we signed the deal in 2012 and inducted atleast one squadron by 2015 than we can exploit the profit of its capabilties. But now FGFA will get one squadron service by 2022. AND FGFA surely is far better than Rafale in any task especially in SEAD, deap penetration and wvr. So what is the profit of wasting 120million dollar per piece while you will have far better than Rafale after 4 years later. Till than mix of mki, lca and super mki can do tasks easily.
One more thing is the low speed of Rafale,which restricting its operational advantage. You know one of the main concern of lca was its low speed. IAF is upgrading itsJaguar's engine due to its low speed, while, it is prime deep penetration aircraft of IAF.
So scrap Rafale and focus on other fighter projects.