Huh, that... just doesn't jive with my experience at all, though I have a newer LG OLED TV. My Chromecast is able to play 4K UHD/HDR content perfectly.

That being said, when I first use a new input on my TV, I sometimes forget that each input has its own profile on my TV, and have to shut off the stupid smooth motion modes and adjust colors, etc. Are you sure this isn't the case on your TV?