Byris, For purposes of making wing joints for model airplanes, epoxy is the better choice because it is good at gap filling. If the joint to be glued was a very good fit and could be well clamped, then a good wood glue, such as the Pica glue you mentioned, would make a very strong joint but the fact is that some of time the time, perhaps most of the time, the joint is not that good and can't be clamped making epoxy the "can't go wrong" choice.