Good info, I appreciate it!
Totally agree on the audio transcoding, but as an “old school” boy I still feel like DLNA is my true fallback… just old habits. Really, is there ever not going to be a server platform I can’t install to handle this stuff from a NAS? 
I tried Shield but it had hiccups with my media equipment and besides some audio sync issues I either had to give up DV support or TrueHD support … just a mismatch with equipment. Was really hoping the AppleTV “passthrough” stuff in TVOS26 would work out but that was not what people were hoping it’d be. Infuse on AppleTV will at least convert TrueHD\DTS-MA to raw LPCM rather than convert to 1mEAC3\640kAC3 respectively but honestly can’t really hear that much difference. 
I was more than happy to use Synology’s DS Video server and client for years. It worked pretty well. I miss my WDTV box sometimes too. That was a workhorse. 
I have installed both before and ran for a bit even with bad matching and they do both work fine. The stripped down interfaces are kinda nice in some ways too. I like Emby over Jellyfin myself - particularly on Roku as Jellyfin Roku client, even v2, is pretty clunky - as Emby was less fiddly to get sorted out (some folks want fiddly, just a preference).
I think one of my biggest QoL features I’d miss you kinda highlighted: Home Screen customization.
Here are those custom rows I mentioned just in more detail (no judging my titles!):
Looking at it now it looks like I gotta fix that first row - it’s in alphabetical order… not random. That’s a newer one I created and hadn’t noticed. 
Edit: if you have to update a row - like I just did - if you update the smart collection filters you have to remove the row from the Home Screen and re-add it for the Home Screen row to use the new filters. It also might hang when you do that but it still goes through.
Those are built using smart collections with some filter parameters (including watch history - and leveraging the watched flag is not the same as watch history for Plex though it’s a little buggy if you flip that flag). Other than those I have Continue Watching and the standard “recently added” for my movie, tv and anime library.
Those rows have drastically reduced decision fatigue when looking for something to watch. You know that thing where you scroll Netflix for half an hour trying to decide what to watch and then just fall asleep anyways? Or navigate to your library to browse the hundreds of titles even if you fiddle with filters and just click click click click row after row? With this, my family pretty much never leaves the Home Screen when trying to decide what to watch (if it isn’t already in continue watching). This is a huge QoL feature for me and Emby and Jellyfin cannot replicate it… yet. Can I live without it? Of course! But I don’t want to… and the New Experience UI doesn’t bug me nearly as much as it bugs others (justifiably) because I almost never navigate away from the Home Screen. If you dig around some of my beta feedback (not really worth the time unless you are super interested) a lot of my commentary there is around UI oddities like wasted space and element weighting and alignment for flow on the Home Screen. 
Emby v5 is supposed to get smart collections and the option to put custom collections on the Home Screen so I’m watching for that… but that’s quite a ways out I think.
I’ve been hoping competition from Emby and Jellyfin would push Plex a bit since they haven’t been the default media center solution for quite some time now but the problem there I think is that Plex and Emby\Jellyfin aren’t competing in the same area anymore. Plex is moving focus and resources towards it’s services and away from local media. Plex is moving more towards fewer granular options and more “do it yourself” (see the upcoming nfo file support) and less customer centric metadata management (all the new artwork restrictions for example) so that their cost cut resources can focus on recurring income streams from their services and local media is not as significant in that area (my lifetime pass was purchased long ago).
Like I said in another post, the new Plex management\philosophy\enshittification, is more likely to move me to another platform but even that is less of a push because they aren’t getting any more money from my several year old lifetime pass.
Oh, and an aspect that some folks might not realize is that Emby\Jellyfin can do audiobooks and ebooks (epub\mobi\azw) and comics (cbr\cbz). That’s something folks have been asking for from Plex but ain’t gonna happen (PlexAmp can kinda do audio books but…)
I like all this discussion on the different features and functions and experiences. I appreciate all the participation from folks who have used them extensively.