Exactly. Even for nations above 15 cities, it’s still a grind.
In order to get both projects, at current market prices, and buy back all the resources I spend, I need to save up around 1 billion (I averaged out the averages of the numbers you gave so it’s not too much or too little), which will take 125 days (4 months) with my income of 8m/day. Keep in mind I have 18 cities and ITC.
So imagine how long it will take for 15-city nations to get the project. They either have to decide whether to buy ITC or not, and in both cases they have to wait longer (to either get back the money/resources spent or to get the money with a lower income).
And as I recall, I earned something ridiculously low, maybe 1-2m/day when I was city 11. To get the ~300-400m need for the first project, it might take a whole year. It’s better to just buy cities normally and increase your revenue so the total time is shortened.
And these numbers are based on the assumption that market prices will stay low, which won’t happen, as everyone will want to make some money on thousands of players buying resources.
TL;DR - Change policy to Manifest Destiny and save up your money.