Bethesda Launcher should let you do something ala GOG Connect...even EA and uPlay allow this to various extent if you have CDKeys or similar codes. Especially on older titles. Like Bethesda's not going to get me to rebuy all the Wolfenstein/Doom/Quake titles on their client, but if you let me bring all those games over from Steam I'll consider your client more, especially when you want me to buy future titles in the franchises on your client. Ubisoft for example, I don't bother with Steam keys anymore, in part because it and uPlay get in fights, but also I might as well have all Far Cry's or Assassin's Creeds or Tom Clancy's in one client, etc. Extra so when the Steam version is barebones and you offer stuff like random ass skins if I play it on your client.
I don't expect the same of Epic, since they aren't the publisher of the games no matter what awesome GOG pulls off in their negotiations, but Bethesda should do this with their games simply to hit a feature parity with Origin and uPlay. And definitely if they're migrating stuff on the backend like Quake Champions and Elder Scrolls Online. I for whatever reason have "paid for" these on Steam (probably from bundles/monthly) and nowhere on Bethesda's client or website does it indicate that my account will cross over and I'll have the "fuller" versions of these games on their client versus just F2P. In the case of these, if I were to play them, especially QC, I might as well just play it through their client rather than layer it under Steam. Siege kept everything when I migrated from Steam/uPlay hell to just uPlay. Do these games? I could look it up, but it doesn't tell me. uPlay made clear you lost no progress in transitioning over to them.
Hell, to hit feature parity with the original days of Steam when you would plug in your Half-Life key and they'd give you like all the add-on content (Blue Shift, Day Of Defeat, TFC, etc.) because why the fuck not.
Even better, it doesn't even indicate whether or not Fallout Shelter of all things has crossplay. I can't trust that it does because a lot of these F2P games have sometimes segmented themselves on PC and especially when they also have mobile versions that are also segmented. I totally suspect that it, and QC and ESO, does use a central account but it doesn't tell me this.
PC Gamers aren't just going to trust that such systems work like this because we've all spent our entire gaming lives running into stupid situations where it doesn't when it should. On games and services far less complex and tied up in corporate reasoning than these clients/storefronts are.