Not true. The PR card allows PRs to enter and leave Canada with the card only. Prior to obtaining the card you need your passport to enter and leave Canada, and if you are from a country that requires you to have a visa to enter Canada, you need a valid visa to enter Canada. The FSW visa is a single entry visa. Just because you have a landing stamp on it doesn't mean they'll let you enter again on the same visa if you leave Canada. They won't! You'd need your PR card to re-enter.
So yes landing makes you a PR, but the card is not just a card. It's absolutely essential for living life as a PR including entering and leaving the country.