Take it from Simon Terodde who is the BL2 all time top scorer. Every time he's in BL2 he tears it up and destroys the competition.... but as soon as he enters the BL, he can't score anything.Schwallacus Shwafta (or others with knowledge about German soccer), what's the reputation and level of 2. Bundesliga? How would relegation affect Pepi's trajectory? Would it be an opportunity for him to prove himself in a more manageable division (like Dike or Harrison in the Championship)? Or is the division not comparable reputation-wise to the Championship and therefore defeating some of the purpose of his wanting to play on a bigger stage, etc.?
BL2 is weird because just about every team in the division could easily gain promotion, or get relegated, at any moment. (Take braunschweig who went from promotion playoff to relegation. Or paderborn who went from BL to BL2 to 3 Liga to regionalliga but went back to 3 liga bc 1860 munich didn't get al icense to BL2 to BL.) I don't think it would be a step back in his development, but look at Sargent. Relegated with Bremen with a not-so-great track record, immediately bought by Norwich.
It might even be good for him, to experience being one of the best teams in the BL2 trying to push for promotion with the other big names like Bremen, Schalke, Hamburg, etc. (if none of them get promoted)