Whilst I agree in looking towards bringing in the next stars rather than throw money away at established players likely to decline and/or not work in the PL (oh, hi there, Arsene. How are you?) - none of the players you mentioned, outside Trippier, fit into the category you’re using them to support. Eriksen, Dier, and Dele all made 30+ appearances in their debut season with 85%+ of those coming in the starting XI.
Only Trippier was brought along slowly and that wasn’t really because the club had plans to groom him. He was brought in as a cheap and steady backup for Walker so we could move on from Naughton. And, despite the PR about Trippier being great and Poch loving him, the club’s singular focus last summer was finding and signing a young wingback to develop that was believed to be Walker’s true heir.
Look, I don’t dislike Trippier and he’s done a very good job and come along better than anyone really believed he would. But this revisionist campaign to recast him as a central figure to the club’s plans? Nah. He was brought in as a solid backup, and played well enough that the club saw him as a serviceable stopgap. Whether Aurier is the next to make RB his or not, we’ll see - but Tripps is a substitute teacher.