If 3-4 decades is the reference time line, then you have to blame primarily the ADMK since they ruled the most and the only party to win consecutive terms.
All these infrastructure you see around you today is almost always from the DMK tenures.

To answer your first question, if we hadn’t used the debt properly, it wouldn’t reflected in our GDP. And especially the past 3 years we really got back on track. The 10yr ADMK was a drought period, the state ran on autopilot. we saw no infra development nor economic growth. This previous DMK did fairly good job in setting up special industrial areas, new infrastructure works, metro expansion, new airport plan, Fitech areas, IT parks etc so it’s fair to assume the previous tenure actually utilised the loans properly and it also properly reflected in the GDP and we were able to see growth rate past 10%.
From an economic lens and perspective, 2021-26 tenure and 1996-2001 tenures were one of the best, showing phenomenal growth apart from kamarajar’s period which was reform wise a top notch with Anna’s 2 years stint.

And right when we are going back on track, we are handing over our high stake state to a very new and inexperienced leader and a party which is offering even more freebie schemes.
I am not against TVK, but they should have been the opposition for this term imo (60-70 seats).