fortnite didnt kill pubg. as far as i can tell pubg is still very popular and in active development by an entirely different company. fortnite has certainly hit the playerbase of pubg but that doesnt make pubg dead.
and no, fortnite isnt very hard. in fact, its pretty easy and has a low skill ceiling. any semi pro csgo player could easily become as good as ur favorite fortnite streamer within a short time.