A fixed cap limits how many coins can exist. It says nothing about what each one trades for, because price is a ratio between supply and demand and only one side of that ratio is capped.

Bitcoin's issuance schedule has been public since the genesis block, and the price still fell hard in every cycle since. If a known cap guaranteed ascent, those drawdowns would not have happened.

What the cap does is remove dilution as a variable. That is real and rare. Indefinite ascent is a different claim and it needs demand that never stops growing.

The supply half of that post is right. The therefore is where it breaks.