I don’t understand the claim that the Scripture are clear but not simple. If they are clear and simple, then obviously no teaching is required and the grasp of them is fairly quick. If they are clear but not simple, then their understanding is not in question, but it will take time to understand them, and probably with teaching aid.
Which obviously leads to the conclusion that any teachers need to be correct, or nearly correct. How do we know that they are? The diversity of Scriptural understanding present right now indicates the error of the clear Scripture position.
I think what perspicuity says is that not all scriptures were created equal. Some of them, like the ones that include basic salvational doctrine, are both clear and simple. A normal person could read those verses and come away with the basic understanding that Christ is God, and was incarnated to come to earth in order to die for our sins, etc.
Now, other scriptures are more difficult to understand, such as Peter's remarks about Paul. They are clear in that all the information is there, but they are not simple because they have to be correctly interpreted to understand the information. The classic example is eschatology.
Which obviously leads to the conclusion that any teachers need to be correct, or nearly correct. How do we know that they are?
Any interpretation, whether from a teacher or from someone's own reading, has to always pass scriptural muster. Of course, problems can easily arise when "new" interpretations are just derived from trusted old interpretations that may not have been correctly interpreted in the first place. That doesn't mean that the truth isn't clearly there (it is), it just means that it may be difficult to discern. For example, I thought about it one time, and I think that the vast majority of all my differences with Apostolic theology REALLY boil down to the interpretation of the very few verses that discuss "bind", "loose", and apostolic succession. We both might think those verses are clear (in opposite directions however :) but if they were simple, then Christianity would certainly have more unity today than it does.