Of course, we already conceded that much of the credit goes to resources available. But he got his team to play above their level often, like against the WI. Pakistan in the 70s had better batting for example.
Captains have a huge say in the makeup of their teams.
Imran literally picked Waqar and Inzi over the heads of the selectors.
Ranatunga stood behind Murali otherwise he may not have continued after 95.
Lloyd decided for the pace quartet as opposed to a regular spinner countering typical convention.
Ganguly backed several youngsters over others and made their careers.
They played better, especially in Pak because Imran played better. And yes, there was an improvement when he was there because he and Javed and co, but also what came before was horrible. But even when Javed took over in-between his stints the results stayed constant.
Re your second point, again, how does that make them actual great captains on the field is my question.
Let's leave out Imran, Lloyd built what was the greatest team ever at the time, but he was never a great captain on the field. Similar with Waugh and Ponting.
Graeme is seen by some as a great captain, but by many as a disaster.
I would wager you all the money in my pockets vs all the money in your pockets that Lloyd was more valuable to that team on the field at 1st than as captain.
Sorry, it takes more than bringing in talent or changing a philosophy to be declared a great captain. I've seen Baggy post on multiple occasions on how not great Immy was as a captain. It's just too subjective, and even wins isn't a great indicator.