While that's true, you still have to execute. And when you see mediocre execution, that's still someone who put in the work.
In the context of games, which are more like creative works fighting for mindshare, an idea is analogous to a business opportunity, which is to say that the idea/opportunity will likely look different once it's actually executed on, and that journey is the valuable part even if it fails.
That's not to discredit someone who is good at identifying opportunities. That's a wonderful skill. But I think the author's take which I agree with is that someone who tries to execute, even with a flawed idea, makes more progress than someone who has an idea/strategy/proposal.
Also I think it's important to point out that this blog post is in the context of (board)game design. Everyone has an idea and the vast majority are under-baked, and the process of designing it and playtesting it is how you calibrate on what other people actually like or find fun. I think that's analogous to, say, tech startups, but game ideas are even cheaper than startup ideas.