The discussion is framed from the perspective of one nation/Columbus because it fits this topic well. People have differing opinions about it, and it’s something most discovered the Americans for most of Europe had no effect? It doesn’t have to be positive. It just has to be an effect. Without this discovery, the world would be exactly the same?
But this is the exact point I'm making. That was the end of my last post: When people say discovery, they absolutely are referring to the discovery doctrine, because that is the material difference between Columbus' "discovery" and Erikson's.
In relation to your comparison with East Africa and China... There is not, as far as I'm aware, a single moment of "discovery" in this context. For example, when did China discover East Africa? Who did the discovery? It wasn't Quian iirc, but I'll confess to being out of my depth here, but I think the murkiness if the point: The thing with this example is that we're talking about a different cultural context, from a culture with a different value system. The European conception of "discovery" is fundamentally unique BECAUSE of ideas like the Discovery Doctrine and Terra Nullius.
For example, you can cite Lewis and Clark as bloodless explorers who journeyed for the sake of it, but an explicit goal of their expedition was to meet Jefferson's desire to declare sovereignty over yet more Native American land. There is an inherent link, culturally, between discovery and ownership. I'm not saying YOU'RE the one that's made that requirement. I'm saying that is the context in which modern Europe operates. It's about dispossession through "discovery", the nullification of entire civilisations. And this is materially distinct from empire building. The Roman Empire was multicultural, whereas Spain immediately set out on a course of cultural elimination and conversation. Not to rule, but to own.
That is why Columbus is the stock answer to "who discovered America", and not Leif Erikson. You have to narrow the parameters to make it make sense, because the "discovery" wasn't even from a European perspective more broadly. The concept of discovery in the context of Columbus is absolutely used in the unspoken frame of colonialism because that is the true distinction of his achievement over the various others who came to America before him. Including those who settled it, which you would think would count as significant.
One can say "well, in the strict dictionary definition of the word it's true IF YOU LIMIT IT to Spain", which, sure, but that is avoiding the very reason why he is cited more strongly as a discoverer in the first place.
Your proposal is to add a qualifier that the discovery is in the context of Spanish history. My proposal is that the discovery is in the context of a bloodstained legacy of colonialism that gave rise to the worst crimes in recorded human history. I don't want people to say "Yeah... He discovered it... For Spain". I want people to admit that the reason the discovery is uniquely celebrated is BECAUSE of the hundreds of years of exploitation that followed, leading eventually to European world dominance. A word isn't just a word. It has weight. Claiming to have discovered something for people like Columbus was to declare ownership. We should refuse it.
Edit: just saw some of your edits. The thing is, you might consider Erikson to have equally discovered America. And you're right! But that is not true for many people. There are no holidays in America celebrating Erikson as far as I know. Right? He is not the stock answer. This is why the issue is contentious, and why it's considered "wrong". You have to zoom out. You're using the word discovery in a strict sense, but I assure you, the broader culture is not. It just isn't. That's why you consider them to be equal explorers but the American elementary schooling system does not.