I switched from Intel 4790K to AMD 5800X 6 months ago. Did I need to do it? In all honesty, probably not. Sure I'm seeing faster load times and generally smoother gameplay when things get busy but given how much more recent the 9900K is compared to my old chip I would expect the margins to be even smaller.
The question I would be asking myself is this - is there anything else I can spend the money on that would enhance the experience more than a hardware upgrade i.e How good is your monitor/audio/peripherals. Could the room you game in do with a fresh lick of paint and some new furniture?
For myself right now I know I've got more chance of being hospitalised by COVID (despite being fully vaccinated) than I have of finding an upgrade for my GTX 1080 so I'm about to have a demo of some nice ATC loudspeakers and an REL T5x subwoofer to potentially upgrade my audio rig. The gfx can wait