The Glasgow giants may have struggled to find the form they enjoyed in previous seasons - and have already shipped a number of points between them so far this term.
But, as far as MacPherson is concerned, the gulf between the Old Firm and the other teams in Scottish football's top flight is still too great for anyone else to sustain a real challenge.
"The winner will come from Rangers or Celtic and it will be like that for some time," he said, as Saints prepare to travel to Celtic Park this weekend.
"They could be split but it would need a club to show a lot of consistency and have a bit of luck in terms of injury and suspensions.
"It would need one of the Old Firm to have a really bad run and I don't mean just for two or three games.
"It would need to be for two or three months to make it possible for one of the other clubs to make up the gap."
MacPherson also refused to buy into talk of a crisis at Celtic, who have a record of just two wins in their last 10 games.
"It's just the nature of the Old Firm," said the Saints boss. "Some people believe there is a crisis at Rangers - and they are sitting top of the table - just because they lost a European game against a far stronger nation in terms of financial clout in the German league.
"That's what happens with the Old Firm and that's why they need strong characters not just in charge of the clubs but playing with them too.
"It's a certain type that is capable of doing that and Tony Mowbray most definitely comes into that bracket, as does Walter Smith. They are strong leaders who know what is required.
"Walter has been at Rangers for a long time now and Tony has played at Celtic so there is nothing taking them by surprise.
"Tony Mowbray knows what being the manager at Celtic entails and given the time and patience he will get it right."
Even so, MacPherson is hoping St Mirren can inflict further misery on Celtic on Saturday and believes his players have what it takes to cause an upset in the east end of Glasgow.
He said: "We are capable of winning at Parkhead, there is no question about that. But what we have to do is defend properly.
"We went to Ibrox and lost a goal within a matter of seconds which made it very difficult for us although we went on to play very well in the game.
"We have to defend properly but we have to have the confidence and belief that we can win the game.
"We need to try to frustrate Celtic but also be positive and try to be creative when we've got the ball."
Celtic 1/4, Draw 9/2, St Mirren 12/1