For whatever reason I don't understand (only Epic, the makers of the Engine, will know) the game runs much slower on Linux. But running the windows version via an emulator gives people great performance. So either way this is the better option.
I would rather not give you a version that is inferior for reasons I cannot change.
I somehow doubt, if you don't understand the causes for the issue, that you've done enough testing to be sure the issue is a problem for all linux users.
If I could obtain both the linux version and the windows version, I could try both (the windows version via wine) and test for myself which is better on my system. In the absence of the linux binary, I would only be able to take your word for it and hope that you are correct.
Even with your assertion that the linux native version isn't as good, for whatever reason, as the windows version, I'm unlikely to purchase the game unless that results in access to both and the choice of which to use.
On the other hand, if you do make the linux version available for us, I would likely purchase immediately, and, if I enjoy the game, I would likely do some deep troubleshooting looking for ways to improve the linux performance (if I perceive a problem in the first place). I'm a weirdo who enjoys software troubleshooting, I sometimes hunt bugs for fun when I get bored of playing games. So, if I get lucky, that could even provide you with some valuable information.
I understand that making the linux native version available here isn't "free" in terms of your time and effort. I'm asking for it anyway, though, because 1) That way I get to play your game, and 2) I am hopeful that you will see a net benefit from expending the effort to make it happen.
P.S.: Just to provide additional clarity about my hesitance to just use the windows version under wine, I have had bad experiences with some software developers abandoning support for games, failing to provide features (including linux support) promised in kickstarters, and other disappointing behavior. I don't know you yet. I look forward to getting to know you, if I buy your game and pay attention to your updates, announcements, patch notes, etc. over time... but in the absence of trust, and the absence of a linux native build listed as supported on the store page, I worry that some future patch will break the game's ability to run under wine, and you will be under no obligation to fix it because I don't meet the OS requirements for the game. Even if you wanted to fix such a bug, fixing a wine compatibility problem is trickier and more time consuming than maintaining the linux native version would be.