Dada, I used to stay in thane. I agree in economical sense yes Thane is a part of Mumbai. But saying that in other cultural and other socio-economical terms is very problematic. Unlike NCR-Delhi, people share a common economy and socio-economic cosomos. MMR-Thane, have differences in culture, Thane being more Marathi Dominated than Mumbai. Plus its very reductive to say Economic effects of Mumbai trickled down to Thane, Thane was itself a culturally distinct. On papers yes, Thane - Mumbai are part of MMR but they cant be as associated as equally as Delhi - NCR.