Insomuch as and Since

Insomuch as conjunction - To the degree that.

Since and insomuch as are semantically related in inasmuch as topic. In some cases you can use "Since" instead the phrase "Insomuch as" as a conjunction or an adjective, when it comes to topics like taking everything in mind.

Since adverb - Earlier than the present time.

Insomuch as and since are semantically related in because topic. You can use "Insomuch as" instead the word "Since" as an adjective or a conjunction or a preposition.