I don't get how a device can be "optimized" for CCA. All a device does is send instructions to the CCA--there is no "streaming" from a phone or tablet to the CCA, as I understand it--the whole idea behind the "casting" was that it takes the load off of the device so you can use it for other things while your media is playing. Imagine trying to stream 4K video--if you had to use the phone to pull the video from the Internet (or your own server), then rebroadcast it from your phone to a Chromecast 4K, there would be huge bandwidth usage along with bogging down the phone to where it would be unusable.
The only thing I can think of is if the app in the phone is sending something (some kind of data and/or instructions maybe?) that might interrupt CCA playback, or not sending the instructions reliably. I see the phone/tablet/browser as being sort of like a DLNA control point, where you're
instructing one device (a renderer, the CCA) to pull data from another (a "server" which in this case could mean the Internet streaming service). I have even had the "connection" between my phone and Pandora get lost (more below), but that did not result in dropouts. With dropouts in the stream, though...the data going straight from a wireless network to any Chromecast device does not even pass through a phone or tablet.
Having said that, I'm tempted to fire up a couple of my ancient phones and see what happens. Got an HTC Thunderbolt here...even an old Motorola Droid (the original with the slide-out keyboard). Can't get much older than that unless it has a hand crank on the side of it.
In my setup, I can tell one of our Google Home units to get the CCA in the kitchen to play one of my Pandora channels by name, and it just plays all on its own. It's obvious the playback is happening in the CCA since I can control its playback from the phone (using the Google Home app) or I can right-click in any Chrome browser window, select "Cast," pick the device, and then pause, stop or control its volume from Chrome. There are also times I have somehow "disconnected" from the CCA--I will start playback in the Pandora app on the phone, and after an hour or so, the CCA is still playing on its own while the Pandora app sits idle (and I can start a 2nd Pandora playback on the phone, separate from what's playing on the CCA), and I have to reconnect the phone to the CCA in order to change stations, which works most of the time but not always.
In my investigations, the wifi router I just bought last year *may* be the culprit for my digital audio woes. So, like you, I may have to buy a device that costs more than the CCA to get the CCA to work acceptably.
The good thing there...IF you change the router, you're improving everything else connected to it. I substantially upgraded over the holidays to "enterprise" level equipment and am getting an incredibly stable signal everywhere in the house now from ONE access point, vs. using two or three previously. I even get strong signals outside, so I could easily stream to my detached garage if I wanted to.
I hear ya, though. I'm the same way about this stuff. That is why I upgraded my network--I liked my old Linksys routers when loaded up with DD-WRT firmware as I could configure things my way, but I had one of them die during a brownout, and didn't want to fuss around trying to find another DD-WRT compatible router, then load a dozen different firmware builds until I found a stable one,
then hope it all worked properly once I got it stabilized.
Even my original first-gen Chromecast was a huge disappointment when I got it. I would have to re-pair it with my network all the time, and it wouldn't stream reliably. I mothballed it for a year or two until I resurrected it for audio-only use on my Oppo (via the HDMI input). I don't know if it was the improved firmware, improved "Home" and "Cast" features, or what, but now it works fine. When I first got it, though, I felt the same way. Everyone was raving about how great it was, and it didn't work properly for me at all. In my case it was probably due to being an early adopter, and expecting it to work perfectly.
A CCA in the right environment
does work well. It's just a shame that your own situation hasn't worked out.
And I know it's not the only device out there that works well for some and not for others--electronic thingies always have a way of finding some crazy situation in which they
do not play nice with others. Been there, done that plenty of times here!