These were our results in the Greg Marshall era (credit OskiOuiOui's blog)
2004 9-8-1 / 0-1
Let us use this to demonstrate a decline. We had a spike in standings in 2004 after our 1-18 season in 2003. If you recall, we won the first several games out of the gate on the arm of Danny McManus and the hands of Demetrius Breedlove. Once they slowed down, the shoddy defense and lacklustre offense combined for disappointment in what remained of the season.
2005 was supposed to be an improvement, but we faltered out of the gate and only managed to win 5 games.
Now, in 2006 we went out and got ourselves Josh Ranek (whose career ended here), George Hudson, Ray Mariuz and we traded for that RB from Regina. In other words we had a talent upgrade.
Now, that is not to say it is ENTIRELY Marshall's fault. Indeed, he was marred by poor coordinators (Kavis and Jamie then PaoPao) and a damaged goods quarterback later on.
However, Marshall continued with said damaged goods quarterback, hired all of his assistants (with the exception of paopao, the nail in the coffin) and was ultimately responsible for the day-to-day operations of this football team.
Under his reign common complaints were: lack of discipline, country club atmosphere, and a general lack of professionalism.
Having destroyed your argument I will conclude by precluding your rebuttal, which will probably be something along the lines of Ron Lancaster. Allow me to intercede on this point by saying that if Ron Lancaster was a problem (which he wasn't, but I don't want to get into it. I know someone will eventually bring it up.) that would suggest a general lack of control by Katz et al over this football club, which would point to a reality contrary to your little conspiracy theory.
Finally: I don't think anyone with a memory that can span more than a few years would conclude the team was by any means in "good shape" when Marshall was fired. In fact, most people were calling for his head, people who had been defending him for two years previous (myself included). He had lost the team, he had lost his talent, and he had lost his ability to win football games at the CFL level. That is what ended his tenure here.