the only parts of Xenoblade 2 that calls back to Xenoblade 1 is at the literal end of the game and a couple lines that would make one go "what's that all about". and then everything after that has no relation to Xenoblade 1. no one is gonna feel like they're missing anything. it's not like Torna
Xeno 2's climax is made 100x more meaningful knowing who "that person" is.