Implying that Epic hasn't been doing everything in its power to claw at Steam's user base. Absolutely no one should be surprised that Epic are doing what they can to not support something that would benefit the Steam Deck, since it would benefit Steam.
Chicken and egg problem, you get no support, so prove you're worth supporting, when you can't get support to be able to prove you're worth supporting. Nice.
But you know what? Let's just play the game for a minute anyway, just for fun. Let's just use some easily available numbers. Steam estimates roughly one percent of players are on Linux currently. Cool, we'll ignore the hardware that's on back order for a few financial quarters, still, that comes with Linux. It's probably not relevant anyway. A quick google estimates XIV as having 35.8 million players as of late December 2021. (The site it sourced its data from says the current subscriber count is currently higher, but I'm trying to math this out in your favor, so I'm sticking with the lower number.) So, one percent of that would still be roughly 358 thousand players. Just to give you the benefit of the doubt, that there's as minimal a financial interest as possible here, let's assume every Linux player is using the cheapest subscriptions, $12.99, though for simplicity's sake, I'm just going to do the math with ~13 / month. The number comes out to $4,654,000 per month from theoretical Linux players. Ahh, chump change, I guess. Not worth looking at.
But hey, let's go a step further. Let's just say that it's not even one percent of subscribers playing on Linux. Let's say it's half that. Half a percent of players, playing Linux. We can just cut that four million down to $2,327,000, still, per month.
We're talking over two million dollars a month over a launcher problem. I think they could afford to take a month of our theoretical existence's money, even half of our theoretical existence's money, and fix what is strictly a launcher-only problem.