I don't think it matters if Copa is an actual Star member or not. At the end of the day their frequent flyer is Onepass, and Onepass will have the agreements with Star carriers.

They already said they are leaving Skyteam just like CO, and it's not like there is a different onepass membership for a Copa flier or a Continental flier. They are all Onepass members, period.

It's just like before Copa became a skyteam associate, you would still earn miles with all skyteam carriers. The only difference was if you had a ff with another skyteam carrier, say Delta, you couldn't earn miles for Copa flights in skymiles. But who cares, if what you need is the miles the other way around.

That said, I usually fly Copa, because of my onepass ff. But the few times I've flown Taca, their service was much better, and the entire experience with TA was much more pleasant than Copa, IMO. But you would def benefit more from a more global ff like Onepass (flying Copa) than Distancia (TA).