Perhaps you are right but you too really got to wonder why none of those big Pangasidae (that you think are MGC) exceed 3'-4' or so it seems from the anglers' photos at places such as Fishing Adventures Thailand and the like.But you really got to wonder where those MGCs come from in exotic fishing lakes. It's certainly not from a wild caught ones.
If its a farm bred, still it can reach tremendous sizes. Wanna get my hands on those.
I don't know much about this topic and I could easily be shown wrong merely with more info from google searches but from that little that I saw I thought that those fish at the fishing tourism lakes could be MGC or some hybrids... yet if they were MGC, they should have been ~7' or larger by now that they have spent a decade or two in those large lakes, where they are fed too.