First off, I don't believe any of your claim without a clear citation, because subdividing parcels is usually considered more profitable than combining them into one big lot. The only time this isn't true is when there's no market for smaller parcels.
Second, you're claiming that big houses command a higher % profit than small houses, which I'd have to see citations for to believe.
Finally, your last claim that you'd be paying "more per sq. ft." is meaningless, because there's a rapidly diminishing marginal utility from additional square feet. If a bigger house brings no more happiness to the homeowner than a normal sized house, then ALL the money paid for that extra square footage is a waste, regardless of whether the "price per square foot" has gone down.
That's all based on the assumption that a larger house is a better investment, which you have no evidence for. A large house drains your finances much faster than a small house - you have higher costs to furnish, higher costs to heat, higher costs to cool, higher costs to clearn, higher insurance costs, higher property taxes, higher repair and maintenance costs. On top of that, you have to spend far more of your own valuable time maintaining a larger house/property than a smaller one. If you're incurring all those extra costs on a regular basis you could easily be losing money. And there's not guarantee that a large home's resale value is going to be better - look at all the McMansions whose prices crashed when McMansions went out of style. For all you know, 20-30 years from now smaller, more sustainable homes are going to be the rage and the market for big homes will be ass.
Breh, you just explicitly described a process that would result in 1/2 as many units being put up, then claim that it doesn't impact the cost of housing because the real problem is....not enough units being put up.
How the hell are these decisions resulting in half as many units not the cause of half as many units? If you built twice as many units on the same land then you wouldn't need to worry about zoning more land for housing, so your claims are inherently contradictory.