Sure, agreed with (a) in general that they both can be causes of decline, but in the specific case of this post, it is amply clear that the wide range of intellectual areas that ancient Greece excelled in (with barely a parallel) was radically narrowed and almost destroyed due to persecution of this knowledge rather than it being restricted to the elite.

I don't understand what you're trying to say with (b).

(a) Euclid and Pythagoras have surviving writings, but the physical applications were lost.

(b) Look at the scientists trying to view Covid accurately.