I just fired up the iTunes Movies app on my AppleTV for the first time so no cache (I only watch my DVD/Blu-Ray rips), and the app started and loaded a full list of movies in a little under 3.5 seconds.
If it takes you minutes, it sounds like PEBKAC.
but, if I hit play, it's instantaneous and I'm surprised at the quality (plus they've upgraded a ton of my purchases to 4k when I bought them at whatever I could)
if I contrast that to local plex, the plex meta-data is instantaneous, but I find it amusing that the appletv videos start more quickly.
plex îs local cache, usually still in memory, apple is building my stuff from legacy iTunes data that I doubt they cache forever for me.
that said, I think I'm ok with the tradeoff for the most part.
If your Plex videos are taking a while to start, might be an issue with your client or server setup. Are the disk drives sleeping so they have to spin up, are they slow for some other reason, etc. My storage is all on spinning disk on 8+ year old hardware and I don't have any issues, except with certain slow clients.
still the slowest of the players I watch. you can use infuse, and often times it is much faster than the plex client against the same server.