How is it a logical conclusion if all celtic have to gain from Rangers is the TV money- which is barely anything to the clubs turnover? I just don't get this line of argument. Celtic fans worldwide don't go to see celtic or buy the numerous shirts (probbably our main source of income) because of rangers believe me.
If Rangers go and remove any remnant of competition that was in the Scottish league, then there's no reason for players to move to Scotland. The league quality degrades over time, you argue that the teams beneath will become more competitive - true, but competitive at a lower level than that between Celtic and Rangers.
The SPL has even less money to distribute in the form prize winnings, so the smaller teams receive even less to spend in transfers and wages. You don't even have 100% attendances right now, you had 83.3% for your last game, and you've had attendances at 50-60% before in league games. Why bother going when your player quality decreases even more? You can argue from a loyalist fan point that fans will go regardless, but it's not even true now.
If TV companies barely see a reason now to invest in Scottish football, there's certainly little benefit without Rangers. You say this is but a pitiful £2m, but why would your worldwide fanbase bother with buying £50 shirts, when they don't even get the TV coverage of you play?
Whenever you think of a high reputation league, you think of its successful teams. La Liga you think of Barca, Madrdid, Valencia etc. Serie A has the Milan teams, Juventus. France has Lyon, OM etc. England has United, Liverpool, Arsenal and now City, Chelsea. Every one of these teams is reliant on their counterparts within the league, whether they want to admit it or not. They're the attractions, they bring in the money and the fans. If you to remove all of the best teams from all of these leagues and form a European super league, how do you think their respective domestic leagues would fare? Well? No. All of the money is drawn to the place where the demand is, Scotland already has low demand, the old firm is essentially all it has. A European super league would draw records sponsorships, TV revenues, but domestically while competition between the remaining is higher, attendances would fall and the overall quality falls as the money dries up.