10 PH farm will get like a net of 5 BTC in 3 years (cause of the halving), while you can buy 9 BTC with the same exact cost of the setup now
How did you get those figures?
9
BTC in today's price is roughly $261,000
Here is a list of some gear prices for (only for bulk)
M30s++ 100th = $1250 , 10ph = $125,000 or 4.3
BTCS19 90th = $750 , 10ph = $85,000 or 2.8
BTCS19 XP 140T = $3400, 10ph = $240,000 or 8.27
BTCM50s 128th= 2,624, 10ph = 205,000 or 7
BTC.
As you see, it could be anywhere between 4.3
BTC to 8.27
BTC, of course, this doesn't take into account the other expences which could easily add up 20-30% to each model.
Now let's review the 5 BTC you assumed they would make.
10PH today makes 0.0262, so without any difficulty increase, in the roughly remaining 340 days for the halving they should make almost 9
BTC.
Now you need to account for power bills, someone with S19xp and 6 cents per kWh which seems to be the average would be paying 35% of that 9
BTC for bills, someone with M30s would be paying close to 50% of that
BTC in power bills.
So the XP guy makes 5.85 before halving (70% into ROI on paper), while the M30s guy makes 4.5 (already hit ROI on paper)
BTC before the halving.
What happens after the halving is unknown, it's safe to assume a 50% drop in
BTC reward if the price goes up i.e, no hashrate drop from the less efficient miners.
Keep in mind that those figures in the previous line are just ROI on paper, it assumes difficulty won't rise for 340 days, no gear fails, no downtime, no monthly/daily expenses, wiring, networking, and everything is not taken into account, which you honestly can't, because to set up 10ph with S19 XP 0.25MW, it could cost anywhere between a few thousand dollars to a few hundred thousand, depending on where you live, so it's impossible to know for sure that exact cost for 10PH for everyone.