Part of the problem is that the question only superficially seemed like it was asking for mere existence. The second paragraph of the original version started talking about what the asker would like or enjoy in a WWII game—clearly, they're asking not because they simply want a yes/no answer to "do they exist?", they actually want to find a game they would enjoy with the intention of playing. The current version of the answer confirms this was the case: they are thinking of running a very specific kind of WWII game and are looking for a system to do it with.
I do think that mere existence is a valid question to ask, to answer your titular question. But I think it will rarely be asked in a valid way—as part of a real problem. I can imagine a researcher asking "does X exist?" and explaining that they're just trying to get a grip on the field, and that could be valid. Answers to that wouldn't be recommendations, just throw out a couple names as evidence for the yes/no part of the answer. Answers that veer into recommendation territory would be off-topic and deletable, keeping the question manageable.
So yes, mere existence is a valid question, but rarely is mere existence actually what someone is asking about.
(Incidentally, now that the question has been refined down to an on-topic problem, I do think your original answer is on-topic and you should consider undeleting it so that it can be upvoted now, for the right reasons.)