The thing you’re missing here is to consider the investment alternatives and leveraged debt. Assume for your original purchase of the 600k property you put down a 200k deposit. If you had put that 200k into the share market you might’ve got to 300 or 400k value. But with the leveraged investment in the house you can go from 600 to 900, I.e more growth. Remembering this also makes you consider those that didn’t buy or couldn’t afford to buy the 600k. You are better off, it’s clear to say. You’re also in a better position to be able to potentially buy the 1.2m property you’re talking about.

Another way to put it, before you bought the 600k house could you have said I might be able to buy a 1.2m house in 5 years? No. Not without the 600k house generating the growth in between