As someone that's been sporting 1440p since 2017, I gotta say it really does feel like a nice sweet spot.
Still using my 1080ti, which does mean that I have to turn down the odd few settings, but nothing major that makes the game look like a Switch version (except for games like Cyberpunk, but that was made with RT in mind, not 1080ti level hw).
Also, playing at 1440p means less jaggies than what I would unusually see when playing at 1080p (also before I upgraded to 1440p, I was playing games that made early use of TAA, and that combined with 1080p was one ugly blurry mess to look at, so with 1440p TAA isn't as bad).
I'm still using a single monitor, but I really would love to someday upgrade to having 2, but I think I'll use my 1440p one as my main for gaming, and pair it with a 1080p monitor for media content/social stuff.
I was thinking about doing this myself as a plan on getting a 1440P monitor to replace my current 1080P one. And like you i was going to use the 1080P one for secondary stuff like browsing the web or getting guides etc while gaming on my main one.
And for anyone who doesnt browse the Steamdeck thread my wife got me a Steamdeck .