Not in terms of passenger footfall, but in terms of main line traffic, it is far more busy than Howrah or Delhi.
Kanpur and Vijayawada handle much more main line traffic (Long distance traffic + Freight traffic) than any other station in the country.
Just going by the passenger trains listed for each station on IRI (As of OCtober 2018), CNB had an average of 197 passenger trains passing through it everyday. BZA at second, with 168 trains per day on an average (and Baroda third, at 148 per day). ...
more... Add to that, practically all the South-East freight traffic and a good chunk of the South-North freight traffic also goes through BZA, making it extremely busy in terms of train movement.
So, yes, it is definitely not the busiest from the perspective of the passengers, but from the perspective of the railway managing the train traffic, BZA is at the top of the list along with stations like CNB and BRC.