Guys if you never played MTG please refrain from these kind of statements which are completely false.
Too bad that I played MtG almost since it came out (1995) and that statement is very much true.
I'm simply not defending the factual power creep that came with the introduction of the Planeswalkers. At the time those were introduced, cards in general simply became more powerful per mana they cost. And there is no such thing as a card that could beat a Planeswalker in terms of bang for the buck.
They always have three abilities, the last of which nearly always is an "I win" button, they cannot be easily gotten rid of (except with some sideboard cards), they become immediate high priority targets and will at the very least cost your opponent significant resources to get rid of (way more so than other cards of the same mana cost would).
All of that for about 3-5 mana on average.
You just can't beat their versatility, so if a Planeswalker exists that fits your deck type, your deck should have that Planeswalker.