There is a way to get Dolby Atmos from the Apple TV with the Arc, but it is not cheap: The HDFury Arcana extracts the audio from the Apple Tv and sends it directly to the Arc while sending the video to the TV. This will give you time to get a new TV down the road.
I got an Arc last Christmas to replace my Playbar and could not wait to get it setup. My HT system was exactly like yours, but I did have a newer Samsung TV with eARC.
I wanted to start fresh, so I reset everything and set up the Arc first by itself. I was very underwhelmed.
The Arc by itself cannot hold a candle to the Playbar! the Playbar just sounded so much better, I almost put it back and thought of using the Arc in my basement!
But then I added the Sub and wow!..what a difference that made! The Arc began to show what it was built for. I got excited again and quickly added the surrounds. With the Arc now as the main speaker, it seemed to breath new life into the old Sub and Play 1s! The sound was so much bigger, it just filled the room so much more that the Playbar could.
I recently swapped out the Play 1s for Era 100s and that was also a great improvement.
The sound from the Arc is still a little harsh in the upper frequencies, so after I did Trueplay, I adjusted the treble to -2 to compensate for that. Now it sounds more like the Playbar so I don't miss it anymore.
The Arc Ultra is out, but there are mixed reviews on it especially when it comes to compatibility with some older speakers. If you can find the Arc for a good price, I would recommend the upgrade. When the dust settles, you won't be disappointed.