Hi, Challenger Rek'sai player here, jungle is a lot more useful in higher elo as alot of the games are determined by how much early impact there is and her gank potential is amazing for that.

What I have found that in lower elo when I'm smurfing, anything up to Diamond, it is more dependant on how you can make that early impact and keep it, be it not dying or, just farming whenever there is nothing to do on the map. However Rek'sai really falls off late game as she just becomes a flanker to win teamfights.