How bad is your upload speed? Most of my x264 and x265 encodes have a total bitrate of around 1.5-2 Mbps. You can’t stream that without transcoding?
Also, have you LOOKED at transcode quality from the other side? It looks TERRIBLE, and it doesn’t significantly reduce your bitrate. I’m telling you, whatever math Plex does to decide whether or not to transcode is USELESS. I’ve seen it transcode x264 videos (that definitely didn’t need to be transcoded) and send them to friends at a HIGHER bitrate, it’s legit insane.
Do what works for you, but Plex transcoding is a bad “feature” that should be avoided at all costs.
EDIT: I’m far from the only one noticing this, the common wisdom is that Plex clients are telling your server to transcode, even when it’s not necessary, and there’s not much you can do about it other than fully turning transcoding off.