IAD to SCL...that's a long way to fly on an A320 or a 737 (even in business).

I can't speak for COPA (no experience), but my AV experiences have varied greatly. Flown their 787 (lie flat) in business from LAX to BOG a few times (I believe this is now a A330 though). Hard product was good. Service was consistently poor to average. Diamond lounge in BOG is fine, clean, nice staff, nothing special though. On my connecting flights from BOG to GRU, I had great crews and service (A330 angled seat). However, I believe these were Avianca Brasil flights which no longer exists, so these would now be staffed by Avianca proper crews and planes.

With the 737 MAX returning, you could see if you could find a COPA flight with this equipment. It has COPA's lie flat bed. They had started to include them in their schedules before the accidents. I suspect they will return.