Its really hard to build a PC equivalent of most unreleased consoles, you have to consider some things:
1 . The hardware isnt going to change for years, maybe 5 years, this means that while MS might be barely at breakeven now, they won't be as the console sales ramp up in year 2 and 3.
2. Now try to build this 'console' again in December of 2019. Im sure you can far surpass it at the same cost by then.
So yea, today its definitely a price to performance beast, but not too long into its life it won't be. So everyone is kinda right here.
(and if you buy one day one, and keep it for 5 years and play online, thats like $250 more dollars on xbl, consoles generate money in different ways, so total lifecycle cost is $750. For $750 its easy to surpass it)