In my opinion for 2D games AIR is unbeatable, but it is also 25 years that I develop in AS so that probably makes a difference. With some careful planning games can be easily resolution/density agnostic.
Also for kiosks AIR has no competition. Especially coupled with Animate that allows for super fast design and prototyping, and if desktop is involved runs very very well. Also for digital signage, with AIR now exporting for Linux, you can operate remotely on machines in background without messing with the video output so in terms of productivity is unbeatable.
UDP works perfectly. I built multiscreen installation with the same app running in display mode on desktops and in management mod ein an iPad, communicating on the local network using UDP and works just seamlessly out of the box.
For multiplayer, there are several platforms that support AS3. Imho, the best one is SmartFox Server, shipping with AS3 libraries. It is a very mature project, abt 20 years old, very well maintained.
Sound management works ok if you do not need BPM precise sync. I know there are ways to sync perfectly sounds working on byte arrays directly but I have never used them. To overcome this on Desktop installations I couple aIR with Max/MSP and communicate to each other using an http api on localhost.
Something I miss dearly, is a maintained OSC library for AS3. I need to use a NodeJS middle tier that converts http calls to OSC.
Ruffle is now use in internet archive for running old sites. It works well. Though, sadly, most of the things I built in the 90s and early 2000s used external configuration files and assets, and since htose were not linked in the html but only in the SWF itself, archive didn't load and archive them so the most advanced things get stuck at loading screen. I am wondering wether, for example for simple casual games, outputting directly for ruffle in the browser might not be an alternative to revive the build once run anywhere paradigm.
Anyway, with its pros and cons, AIR is a swiss knife that allows for incredible outputs in no time. Any agency should seriously consider it. I remember abt 20 years ago just listing ActionScript in your skills would have landed gigs in no time 🙂 good memories...