No, my English teacher told us before that it is possible to get an A in the Junior Cert English exam without reading a lot of books or novels but the vocab would help to expand on answers which would mean there would be a higher chance of you getting an A!
There are no As in the new junior cycle. The highest grade is a Distinction. There are 3 strands to the new course oral language, reading & writing so reading is important. You are expected to have studied at least 2 novels during 2nd/3rd year and to have read a wide variety of other texts.