The ASUS TUF Gaming VG27AQL1A panel is Innolux's M270KCJ.
The ASUS ROG Strix XG279Q panel is AU Optronic's M270DAN06.6.
The Dell S2721DGF panel is LG's LM270WQA-SSA2.
The LG 27GN850-B panel is LG's LM270WQA-SSA1.
That's just the panels.
Yeah there are varying levels of:
refresh rate,
contrast rating,
brightness rating,
color accuracy at factory calibration (eg: sRGB or DCI P3 or whatever-the-fuck-ASUS-feels-like-doing),
color support (eg: 6-bit + FRC ("fake" 8-bit), 8-bit, 8-bit + FRC ("fake" 10-bit), 10-bit)
peripheral support (eg: USB hub),
ergonomics (eg: adjustable height),
bezel size,
motion blur handling (eg: ghosting/reverse-ghosting, at low- and high-refresh rates),
adaptive sync support (eg: FreeSync/GSync compatible vs official GSync module)
HDR rating (eg: HDR10 vs HDR1000)
DisplayPort High Bit-Rate (HBR)
HDMI 2.0 (or 2.1 Soon(TM))
USB Type-C (including daisy-chaining)
internal vs external power brick
etc etc etc
There's a lot of checkboxes to go through and the prices go all the way up and down the scale.
source:
https://www.reddit.com/r/Monitors/comments/i95mlk/what_are_the_differences_between_these_1440p/