I think one of the slot providers that lets you do this is Booming or Betsoft, not sure if it's both of them but i'm sure that the name of the provider is starting with the letter "B" since these are the providers that most casinos have back then.
This is interesting- was the discussion backed with evidence and facts? In addition, did the gambling websites disclose such information to the public or was it purely based on his gathered data and information? I am curious as to how the methodology of such research went as this can either make or break a gambling website's profit in the long-run.
As regards to OP's question, I really doubt that a gambling website would disclose such important piece of information to the public. Preferably, slot machines that have high RTP are the ones to be preferred if you plan on gambling long-term. But this could definitely hurt the gambling business as this would be prejudicial on their part.