That's precisely the sort of bubble economics that the parent was objecting to. The objection is to speculation as opposed to investment - investment expects a steady return based on real profits/assets, speculation expects a greater fool to come along later and pay more for this asset, regardless of what it might actually be worth based on revenue/assets alone.

In a bubble (tulips, houses, stock markets) there seems to be an unending supply of greater fools, until all of a sudden there isn't, and someone (who of course expected to find some other fool to sell to) is left picking up the tab for assets which are now close to worthless.

If your valuations are based on what someone else might pay in future, you are speculating, and will be lucky if you manage to get out before other people realise the assets you have bought are not worth $1B or whatever you paid for them. If on the other hand you bought because there is a steady income stream from an investment which will eventually pay off the investment and add returns, and thus underpins the price, you don't have to worry about whether this is a bubble or not.