Noam Chomsky:
"The interest of linguists, as linguists, in universal language was based on an illusion, which linguists had but no longer have. That was the illusion that Esperanto is a language, and it isn’t. Yeah, Esperanto has a couple of hints that people who know language can use based on their own linguistic knowledge to make a language out of it, but nobody can tell you what the rules of Esperanto are. If they could tell you that, they could tell you what the rules of Spanish are, and that turns out to be an extremely hard problem, a hard problem of the sciences, to find out what’s really in the head of a Spanish speaker that enables them to speak and understand and think the way they do. That’s a problem at the edge of science. I mean, a Spanish speaker knows it intuitively, but that doesn’t help. I mean, a desert ant knows how to navigate, but that doesn’t help the insect scientist. [...] To be puzzled by simple questions is a very hard step, and it’s the first step in science, really. And the same is true about the nature of Esperanto, or Spanish, on which it’s based, and so on. We don’t know the answers to the questions of what the principles of Esperanto do because if we did, we would know the answer to how language works, and that’s much harder than knowing how a desert ant navigates, which is hard enough. So, now it is understood that Esperanto is not a language. It’s just parasitic on other languages."
"But there are people, serious scholars, who think that everyone should speak Esperanto, 'cause it's so simple, that there's an illusion that Esperanto is a language. Esperanto is not a language. It's a couple of simple rules which pre-suppose that you know Romance languages, and then you use all your knowledge of Romance languages to sort of figure out what's going on. But none of this means anything."
Trying to talk about which languages are "simpler" or "easier" in a vacuum completely misses the relationship between language, culture, and human action. I'll take it that Esperanto is "simpler" than English, based on what you've said and what Chomsky says here, but this doesn't matter. You're taking a value-free statement about the "simplicity" of something and turning it into a value judgement about "better" or "worse" for a given problem. This is called the "is-ought fallacy." What you're doing is like saying that math equation x is simpler than equation y, and that we should therefore use equation x. It doesn't make sense.
So, to try to argue for Esperanto in TF2, it can't be based on how "simple" it is, or any of the factual qualities of Esperanto, since that's fallacious. You might ask: "How am I supposed to argue in favor of Esperanto, then?" and that's my point: you can't. We don't speak because we have some goal in mind (like "simplicity"), because the ability to think about goals like simplicity requires the ability to speak in the first place. Therefore, any argument based on some abstract "quality" of a language like simplicity is circular and nonsensical.
The only argument you can make in favor of a language cannot be based on the "language itself," for the reasons I've explained, but because of some "outside reality," i.e., "Chinese could be useful to learn in case we go to war with China," or "You should learn ancient Greek so you can read Plato in his own words," or "You should learn Esperanto because it's fun." That is, an explanation of the "practicality" or "usefulness" of a language can only be based on some pre-existing, empirical judgement that we choose to make ourselves, or that rests on some outside source of "usefulness," like the desire to read Plato. But how does this look in TF2? People in Europe communicate using English in TF2 because many of them already speak English. If enough of them already communicated using Esperanto, then people would learn Esperanto. Notice how the "language in and of itself" (if such a thing even exists) doesn't come into play here.
Furthermore, the very fact that non-native speakers choose to speak English when playing TF2 proves that it's the best option for communication right now. The term for this in economics is called "revealed preference." As David Gordon writes, "When you make a choice, it’s usually among a few options. The choice is an action, and the action demonstrates, or reveals, that the option, or preference, that you choose ranks higher than the competing options." People in Europe have chosen English over Esperanto, and therefore, for whatever reason, they prefer to speak English over Esperanto. I think this is the idea Brody was getting across when he said you were rejecting the "human impact on the use... of things like language." And what could be more human than Europeans' choice to speak English over the other options? By saying something like "Esperanto should be the language of EU competitive," you're saying that Europeans themselves would prefer Esperanto over English. I ask: do they? They have chosen English despite the difficulties you've mentioned. As James Buchanan wrote:
"The market economy, as an aggregation, neither maximizes nor minimizes anything. It simply allows participants to pursue that which they value, subject to the preferences and endowments of others, and within the constraints of general “rules of the game” that allow, and provide incentives for, individuals to try out new ways of doing things. There is simply no “external,” independently defined objective against which the results of market processes can be evaluated."
You can apply what he's saying here to the "market of second languages" in Europe, or even about language itself. It would read like: "Language neither maximizes nor minimizes anything. There is simply no 'external,' independently defined objective against which language can be evaluated."
These are some thoughts I wanted to give on this topic.