While I won't defend the business practices of our telecom operators, I think there are some points that should be noted:
1. US ARPU might be dropping, and ours might be increasing, but we still have one of the lowest network charges in the world.
2. Equipment costs are almost equivalent everywhere. With lower ARPU, our operators don't have the liquidity to install more hardware based on requirements, thus our average speeds are slower.
3. Speeds depend on density. In major cities like Mumbai, which are extremely dense, we require tons of towers to handle all the load. This goes back to point 2, where our lower revenues mean fewer hardware installations.
In cities with lower density, speeds are fine (I get 700-900mbps consistently at my tier 2 native).
4. Speeds might be slower than 4G because more people in our country are going online now (along with vastly more data usage). This increases load which decreases speeds.
5. 5G was developed to handle more load than 4G. Speed increases were not the main motivation (but might still be present).
Speed increases come from installing more hardware and using higher frequencies like mmWave (both of which are lacking in India).
Hence I wouldn't say it was marketing to sell 5G equipment. 5G is doing what it was intended to do.
If the same hardware installations were used with 4G, you'd see much slower speeds because of the increased load.
EDIT: To add to this, generational leaps won't come with using the same frequencies as we are now. 4G/5G/6G are all being developed to handle more load with the same requirements. Generational speed leaps (and lower latencies) will only come with using higher frequencies of the spectrum.
But those come with their own challenges (the higher you go, the more losses you have, which makes things like mmWave essentially Line-Of-Sight as of now).