Obscure? Hardly. As for 'primary usage', the usage of the 'first' definition is falling into desuitude- sorry, disuse, since you have trouble with big words- and the 'secondary' scientific definition is used quite often in, wouldn't ya know it, scientific contexts, or in other words, quite often.

Seriously, Lychon, you have no point to make. The definition I used was correct, ESPECIALLY since we are dealing with theories, the situation in which it is meant to be invoked.

Next, no, insufficient does not fit the meaning of the existing sentence at all, seeing as it means the inability to suffice, and my original phrase was about a an explanation that was sufficient without needless additional terms.

Lastly, yes, you are being a nitpicker.