Use of yet and despite

GRE Verbal Problem Solving
1

Modern agricultural practices have been extremely successful in increasing the productivity of major food crops, yet despite heavy use of pesticides, _____ losses to diseases and insect pests are sustained each year.

I have just started the 2 months plan from today and learnt about math strategy from the 1st verbal video in Day 1 section. Here, in the above question, there is the use of yet and despite which are both contrast words. Doesn’t both contrast words yield a positive tone or be positive ??

2

If you break down the sentence, the first part says “Modern agricultural practices have been extremely successful”, which is a good thing, yet serves as the division word and the second part should contrast by saying “Some Modern agricultural practice” are not successful. So a good guess for the blank would be “large”. Do correct me if I am wrong.