They may be good in very specific or very niche situations but you would almost never seriously consider putting them in a competitive deck
Now, Ill grant that maybe saying that a planeswalker is good on an empty battlefield isnt that meaningful of a statement, as most planeswalkers are good on empty battlefields, but Oko only costs three mana and Oko is green, which means its far more likely than most planeswalkers to be cast on an empty battlefield
I have done quite a lot on why this card is so good so will keep this super brief
P/T Number 207a Language English Legal Formats Alchemy, Brawl, Commander, Competitive Brawl, Historic, Legacy, Modern, Pioneer, Standard, Timeless, Vintage Rulings (10/2/2025) An ability that triggers "whenever you waterbend" triggers whenever you pay a waterbend cost, regardless of how you paid that cost
Just be aware that players who play competitively will build the minimum requirement to raise their odds of drawing their best cards