Maybe it is just the devices I have, but I've had the higher end 4K-capable Roku boxes before I eventually got all Roku TVs. I would say the experience with my Roku TVs (TCL, Phillips, and Sharp) has been the best. Nothing slow about them.
I don't try to do anything like run a console emulator on them though. Just watching streaming channels and YouTube TV.
I wish I could come back and ask you how they perform after a couple more years of "software updates" from the app providers. Considering, too, that they will also be vibe-coding them from here on out.
IDK about the specs on yours, but even things like bloated sizes of apps themselves on disk can become a problem. What happens when the OS and the apps inevitably go up in size such that the 8GB or whatever TCL has decided to give you cannot hold the OS, Netflix, Disney+, and HBO at the same time? They don't just let you stay on old versions anymore, either.
I have a 10 year old 4k Roku TV that works a good as new. The Roku app API is severely limited. The upside of that is that it discourages webdev bloat.
Interesting. Honestly I had never considered that angle. Given that they really ought not to need anything but simple navigation of lists and grids to build a streaming app that is actually usable and fast, not whatever the Youtube App (330MB) and Netflix (183MB) are wasting my phone's space on... now I'm wondering if this forced parsimony imposed on the developers could be a reason to give Roku a try again. I admit it's been over a decade since I used a Roku regularly.
I don't try to do anything like run a console emulator on them though. Just watching streaming channels and YouTube TV.