(1) I believe that you are 100% correct: it is a linking verb (some books
call it a copula). It is something like the equals symbol ( = ).
Absence of faith = worse than slavery.
Worse than slavery = absence of faith.
Kindly remember that sometimes "is" is a full verb that means something
like "to exist":
The baby is on the bed. (Tells you the location of the baby. That is,
where the baby "exists.")
Have a nice day!