You’d lose the handshake that is part of CEC. That means the Arc would not be telling the TV what kind of signal it can process. Nor can the Arc communicate with the TV regarding volume, although the Arc would still work worth an IR remote. Finally, you’d be restricted to Dolby Digital only, which means no Atmos. There just isn’t enough bandwidth on an optical connection for Dolby Digital Plus, or TrueHD/MAT which are required for Atmos.
On the other hand, I had mine set up that way for a couple of weeks. It still sounded nicer than my PLAYBARs, and the width helps, too.
This LG C7/Sonos Arc user reported Dolby Atmos audio using an Apple TV 4K:
https://www.reddit.com/r/sonos/comments/h0grdp/lg_c7_appletv_4k_arc_working_dolby_atmos/
This would definitely not be possible with the Arc connected via optical.
Here is another thread with a few more C7 users getting Dolby Atmos with the Arc:
Have you considered using an external HDMI switch for some of the other devices? A bit of aggravation to have to switch them instead of just using the TV remote but it might be good enough.