Why is it that when people compare coins, they bring up what the "market cap" would have to be in order to project a price? Why does this matter, if it's just coin price x number of coins?
Why would one coin not be able to achieve a particular market cap?
That's mostly useless metric
You feel as if it is telling you something but it isn't. It is a sort of optical illusion which makes you believe in something which is not really there. And it becomes particularly misleading and deceiving when people start drawing conclusions on its basis. For example, when Bitcoin recently flash crashed to below 2,000 dollars per coin, its market cap diminished by 4B dollars, and some people here seriously believed that these monies were real, as if literally 4 billion dollars had been withdrawn from Bitcoin. This example shows it pretty unambiguously how fake is this metric
It's not fake or useless, you just need to understand how to relate it.
obviously you can't base your investment on that parameter alone, but you can use it with others.
with new coins and small amounts it might be misleading,
but when going to big numbers over serious amount of time it is much more transparent.