Pressley had a decent half a season too (arguably better given the circumstances). The only difference is Robins had the sense to jump while he could!
We've had many managers who've had spurts. Black, Adams, Dowie... hell even Reid started alright until we sold Davenport from under him. Black and Robins survive with reputations intact as much because they were lucky enough not to fall victim to the insidious destruction that lies within.
You're preaching to the choir man, I've made the exact same argument, we've had no manager who has performed over a full season or more since Strachan really. Edit: and even his good season had some serious flaws.
Edit 2: To expand on this a bit:
I know both Richardson and Ranson get a fair amount of stick on here (as well as Paul Fletcher), a lot of it fair, but one thing that they did is set a course for the club. It may have been overreaching, or the wrong course at the wrong time, but it let everyone in the club know what the plan was and what the expectations were.
This allows for a fully congruent club, with everyone pulling in the same direction. If you disagree with the vision you can shape up or ship out, it gives the organisation a cohesive language and direction. Whether particular people are competent, or whether the direction as a whole is correct, is a different issue, it's about the effectiveness of it as a management strategy.
Compare this to the stated aims of Fisher, Delieu <sp?> or McGinnity. They were solely about administration of the club, the wage bill, the finances, income streams, the stadium, etc, etc. What, realistically, can a player, manager, tea lady, etc, do about those aims? Take a pay cut? Pick up less win bonuses (j/k for the tin foil hat wearers)? And even if people do buy into this vision, what energy does it create around the club? Is that the energy you want to bring onto a football pitch?
There's no role for anyone else outside of the board in this vision. The problem then is that fans don't really want to buy into this vision, so you have to sell the sizzle (as the sausage has been cut for budget reasons) and talk the talk about say, becoming a stable club, except the budget dictates that you can't build a stable team as good players leave and others need to go quickly for cost reasons. You can't realistically claim you're aiming for promotion, so what do players talk about in the papers? What does the manager talk about? Because it's not your focus the message about where the club is going on the pitch becomes fuzzy. So your message isn't congruent, it doesn't feel authentic, and people are turned off by that on a deep level (think fake salespeople, or creepy realistic robots).
Even if your real aim is to cut costs, you need to achieve it with an inspirational vision that the entire club can rally around. That's very hard to do when there's no chance of claiming you're going for promotion, and the club is under no real immediate threat as Sisu can keep it going as long as they like. So you get this grey blob of apathy which is where we are now.
tl;dr: The club needs leadership from the top before changing the middle management will be effective.