Does using a Roku provide better picture over using TV built-in apps?

Hello all, I've occasionally seen in TV based communities that using a streaming stick like Roku provides noticeably better picture quality over using the built in TV apps. I currently have a 75 inch Hisense U6K, and was curious if:

1. People have found this to be true (I use YTTV, Disney +, and Netflix)
2. If true, would it be worth the $98 for the 4k/hdr/atmos Roku?
3. If not Roku, are there any other recommendations?

Thanks!