Blood offhand weapon

My favorite combination is Chaos/Blood. I am currently running Eldritch Tome for my Blood offhand. What are your thoughts on using Lost Tome of Lies instead to get the free passives, which will allow me more passives for Chaos to improve Paradox generation?

I can’t help you with crunching numbers, but if you have both weapons you could try them out at seasonal megabosses, should you find some that stand still. EF buff should make the difference in item levels irrelevant, but extraordinary effects will still work.
My completely uneducated guess in this situation would be that anything that makes your mainhand stronger is better.

IIRC none of your perks apply to your non-main (can somebody clarify please?). Unless you routinely switch main in content, it’s not doing much other than changing your stats.

If I am correct, then the Tome is the better build. But, as I say, it depends on whether I am right or not, and your playstyle / how often you switch ;).