I have 2 good friends whom own gyms now and another buddy just bought a new gym in Florida, and I knew another guy years back who owned a decent gym, all of them said the same thing, you make your money on the Supplements you sell there, and the shakes and shit you make behind the counter, thats where the money is at!
I know another guy who owns a Crossfit gym and they have been breaking even for years now, and he reached out to me last year about selling Supplements there in his crossfit warehouse as I suppose he figured out that is where you make all your money.
Crossfit is fading no doubt about it!
Personally, I would go with a NICHE type of gym, and my niche would be the Hardcore lifters! As they are loyal, and they feed their bodies with supplements you can sell at the gym. And Personal Training out here in Jersey has been phenomenal money making machine for the last 17 years, as I know guys who have brand new Nazi Sleds and Jags, not to mention New Houses all built from PT money. I don't know how the market is in other states for Personal training, but I know out here it is huge.
Anyhow, I think you need a hardcore gym these days to make money, as you can not compete with Planet fitness or Retro for that matter, and Retro needs to see 1 Million Dollars in Assets before they even let you look at the Franchise paper work lol,
If it were me, I would go with a Bodybuilding Dungeon that smelled like free weights, chalk and rubber matting when you walked through the door!