Whilst everyone knows that only one team in Glasgow can be on top at any given moment, try tell that to any Rangers or Celtic fan when they’re in the midst of a downturn. There have been several times over the course of the Old Firm duopoly where one side has dominated the other and we’ve been told it’s a never-ending cycle destined for eternity. And each and every time, such apocalyptic doomsday mongering has been proven reality only in the minds of gloating journalists, fans and ex-players. The reality is that in Glasgow’s goldfish bowl you’re never more than one week out from catastrophe or…