You have a valid point, but the audience for your comments is the developers of those channels. That developer is not Roku. Netflix and Plex are responsible for their own channels for Roku devices.
That said, I've never seen that sort of load times on any of my Roku devices. I don't think I've ever seen more than 10 seconds to load any channel on a Roku. I'm not counting my ancient 2 XS, which can barely run itself, let alone any channel.
I don't have a Premiere+, so I can't make a direct comparison with your results. I'm sitting in front of my Ultra 4800 at the moment, so that's the one I will test. Of course, this is the newest and most powerful Roku player yet built.
Opening Netflix to reach the user selection window took at most 3 seconds. I almost couldn't catch it in time, so I had to do it a second time. Plex took a full 10 seconds, but Plex is a slow loader on any device I have, including the web browser on the Plex server itself.
I can't say why it's taking so long on your device(s), but it doesn't match my experience here. While I have a Gigabit Ethernet network in my home, my Internet connection is "only" 108 Mbps. Of course, Plex shouldn't be using the Internet to load, since the server is on the same internal network. But I suppose it might have some authentication that is performed when it first loads. And that might go to the Plex servers, and might explain why it is slower than most channels to load.
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