Only thing that is going to bring more players into the game now that is noticeable is to have another commercial on TV and/or youtube and Rumble. This is simply no marketing at all for this game and I still believe most haven't heard of it. It's a very niche game and the subscription prevents many people from trying the game again in the MA after a couple of months. People just aren't gonna pay $15 if they maybe want to play the game just to try it again where most of the action is.
You're an accounting guy, right? So you understand ROI.
You can look at your current conversion rate based off your normal organic traffic. Lets be generous and call that a full 1%. You can then looks at estimates of market size your ad platform might likely give you exposure to, and then look at the ad cost and make a reasonable guess to if that would be a positive or negative ROI.
If the math suggests there is no possibility of a positive ROI based on any of the data you have, then advertising would be an expensive hobby.
In previous years when he was advertising, he may have had 12% conversion rate. That may have given him a positive ROI. He had reason to believe it would turn a profit to make that ad spend.
At 1% the numbers may not work. I doubt HT has wads of cash to throw at something his data tells him can not be mathematically profitable. He would only advertise his way into bankruptcy.
You have two obvious choices.
1. Find cheaper advertising.
2. Improve your organic conversion rate so that you have a reasonable chance to profit from investing in ads.
The discussion of things like how FTP and other option might effect conversion rate is to find a solution to raise the conversion rate so that it is rational to try and throw ad money at it because you will then have data that suggests it will have a positive ROI.
I assure you if he had data that suggested he had high enough conversion rate to make ads profitable, he would move heaven and earth and go sell blood plasma to raise the money to buy ads. Until he has a better conversion rate, he would be better off burning that cash in his fireplace to at least save on heating bills.