How many NITs are better than IITM Gwalior?

Your question is not relevant because even new colleges are growing fast in terms of curriculum, culture, and placements. You cannot deny the fact that only the top 7-8 NITs are doing than IIITM Gwalior. It is just below NIT Bhopal in terms of CS/IT education.

Apart from that, NITs offer core branches too but IIITM Gwalior only offers CSE/IT so the comparison would be based on only these.

For Coding Culture - It would be better than almost all NITs as this is based on their participation in ICPC (Olympic for coding).

For Curriculum - IIITs have a better curriculum than NITs in general and they are more updated. Like NIT Kurukshetra, Computer engineering is very much focused on hardware.

Placement Scenario - IIITM Gwalior is equal to NIT Kurukshetra having an average placement.

In the case of reputation among the IT industry, IIITM Gwalior would be equal to NIT Bhopal. So, yes IIITM Gwalior is doing really well. If you do opt for it, it is a worthy choice.