Agreed. I have two monitors claiming HDR400 support, you never ever want to turn it on as it looks worse than sticking to SDR. Especially as my TV is OLED.
You don't necessarily need 1000 nits brightness for it to look good, but you absolutely need a LOT of dimming zones, which is only available on monitors costing as much as my TV.
I had to increase to 28" to get a 4K 144Hz monitor as apparently 24" has fallen out of fashion. I'm somewhat glad as my eyesight is getting worse and the pandemic has meant I can't get new glasses but still, monitor sizes are getting a bit crazy when the best ones only come in 32". That's FAR too large for desktop use and if you're only gaming, an OLED TV makes a lot more sense in that price range.