yes, season 5 is a bit of a filler season. It picks up in seasons 6 and 7. (comedy-wise the best are by far S6 episodes 4 and 21 🤣 can't wait till you get there) Also the slow character development is essential and well done in my opinion, because it makes the last seasons so great and not boring or random. Big Bang has a well-written, plausible ending and wasn't somehow made up in a short time because an actor didn't renew his contract or something as it happens sometimes with other sitcoms.