By believing a source rather than deciding by yourself what is correct, you take the wrong path. This is not science, it's religion.
If the model you promote wants faster alpha decay for lighter nuclei, despite alpha decay appears when nuclei are heavy enough, then the model is wrong. This is clear enough that you should be able to decide it by yourself. This is your job as a scientist, whether the source is MIT or anything else.
That alphas don't move within nuclei is less obvious, but it would be useful for you to understand. It's the same situation as for electrons in atoms: they would radiate light and lose energy, which doesn't happen, hence wrong model. QM says "stationary solution" as a solution. Any course that suggests that nucleons move in an unexcited nucleus gives a bad service to the students.
As for the speed of alpha decay, you might give a thought at the electrostatic repulsion among protons. Check the "liquid drop model", it's incomplete but at least it goes in the right direction.