Following the 4-0 defeat to Celtic, the Dons boss has come under pressure, but the club's record goalscorer, who has been inducted into the SFA Hall of Fame, believes he should be judged at the end of the season.
Harper said: "If Aberdeen finish third or fourth and get into Europe it will be a successful season. My prediction is Derek McInnes will still be Aberdeen manager at the end of the season and planning for the next campaign and I think people have to be realistic.
“The problem for Aberdeen and Derek McInnes is you have two teams who can spent millions on players and the rest are fighting for third place. Given the financial gulf between the Old Firm and Aberdeen it’s unrealistic to expect Derek and Aberdeen to be able to bridge that.
“It’s a different supporter now with social media. Criticism becomes personal. If you had people coming up and saying this stuff to you in person in the past you would have knocked them out. But it’s different now and Derek will have to bear the brunt of it.
“The bottom line is their rivals have far greater budgets and that’s why only Celtic or Rangers can win the league."
However, Aberdeen fans are not asking for McInnes to have the side challenging for the title. They do, however, want their team to be doing a hell of a lot better than they are just now. They are currently fifth and playing unimaginative football.
By and large, football supporters are not actually that demanding really. The Dons support realise the gulf in finances and the challenges in place to compete with the Old Firm. But for a team with arguably the third-biggest budget, they want that to be demonstrated on the pitch. In addition, at least showing signs of progress and playing football that excites rather than exacerbates.
When it comes to Celtic and Rangers games they simply want to see their team be competitive. That has not been the case this campaign at all. In two matches they have shipped nine goals and barely looked like laying a glove on either Celtic or Rangers.
Against Neil Lennon's side at Pittodrie on Sunday there was a spell in the first half where Celtic kept the ball for 2 minutes 30 seconds without an Aberdeen player getting a touch. It was taking passive to the extremes.
It enraged fans watching on, eager to see Aberdeen making it uncomfortable for the league leaders the way Livingston did.
Another statistic in which to hit the Dons with was the number of shots attempted on Saturday. They had just one in the whole game and it didn't go on target. It is only the second time since 2000/2001 that Aberdeen have had only one effort at goal at Pittodrie, according to one Scottish football stats analyst. The other occasion was a 5-1 home defeat to St Johnstone.
It feeds into a worrying trend this season where it is easy to see why the club's support are so frustrated.
Only Hamilton have had fewer shots this season than Aberdeen's 86. For context, bottom of the table St Johnstone have had 112. When it comes to touches in the opposition box, again, only Hamilton have had fewer.
It is no real surprise when you consider Aberdeen have had a real dearth of creativity and panache to their attacking play. They don't pass the ball into dangerous areas or have the ingenuity to unlock defences. They have passed the ball into the final third more than only three other teams - all are currently bottom six.
It is not a revelation that Aberdeen need to improve. And it starts in attack, showing more gumption and a more willingness to engage and confront opponents.