He's played around the 1700 min mark in the league per season in the last 2 seasons for Salzburg, and less the season before. Players like Milner for Liverpool played that sort of minutes last season, even Keita with all his injury troubles played around 1400 mins in the league last season.
So what I am saying is, players who are not guaranteed starters, still end up playing a good amount of minutes even for teams such as Liverpool, add in cup games, and European games, he'd likely be playing in plenty of matches. So the choice is for the player - does he want to take a smaller step up and maybe go to the Bundesliga first, or just take that bigger step and go to Liverpool. If he backs himself, then why not.