HDMI 2.1 is perfectly capable of 1440p and 4K gaming ...
HDMI 2.1 has several aces up its sleeve, but DP still rules PC gaming ...
You can also drive multiple monitors from one DisplayPort connection, rather than having to use multiple ports, which is handy. Laptops can even send DisplayPort signals through a USB-C port.
Monitor makers have been slow to adopt DisplayPort 2.1/2.1a connectivity, which is a bummer if you're in urgent need of a display and want to future-proof your setup (as much as possible, anyway—true ...