You seem to be under the illusion that there is any real science to appointing managers. In any walk of life. I've worked under many managers and seen many managers hired for various reasons and fired for various reasons. Some came with great experience, others promoted from within with success and others promoted from within despite glaring evidence that they were useless. Some of the useless ones even turned out to be quite good at managing.
In reality, luck has a gigantic role to play on all levels. Whether they fit in, whether certain players hit a run of form, luck in the transfer window, settling on a system that works, having one or two in the background that hold things together etc. Having Robson in as interim helps to root out some of the wider problems too. Things that can be attributed to something that isn't the manager, that can be weeded out before a new guy comes in. I guess that's always a benefit of an interim appointment, but it has to be weighed against the danger that he might do really well and fans will always use hindsight to suggest we should have just kept him.
You mention not having a guy lined up too, I just don't think that's a thing. The club should always go through a process, even just to rule out other options. You never know who might throw their CV in. You also might have targeted a manager who is with a club that then goes on a run of shite performances and you have to rethink. Any manager that's jobless will likely have just done that too. However, it may just be that you believe that succession planning within the club in both players and management staff is always the correct way to go (if circumstances allow). I generally think it's a good thing, and I'd be quite pleased if we're trying it. The hiring of an experienced coach to see the process through is also sensible. I also don't think it's necessary to explicitly announce that approach either, when you can ease Robson in with less external pressure (he'll know, obviously, so he'll have that internal pressure) and give him time and support to establish himself.
I genuinely don't know enough about non SPFL managers, so I'd be quite happy if a more mature, more disciplined (with age) Robson is given the opportunity to take the role.