Seems like IS wants to lean heavily on old characters since they have had good success with Heroes, and have tried this before with awakening. I don't really get it myself, as while these characters are technically in these games, they are kind of empty characters without their own story and world. Like Ike is in Engage, but without Tellius and his allies, he doesn't really have real character. This is fine for heroes, which is just a mobile game where the story doesn't really matter, but in mainline titles, it detracts from the world. I think the series would be strengthened by taking a step back and focussing on the story they are trying to tell (3H was good in this regard).
I did really like the skills that came with the emblems and the associated gameplay improvements. Kind of wish they were locked to certain characters as it makes everyone seem more unique and brings more utility to certain characters. I kept benching people this game because stronger characters just kept coming, and there was no punishment in terms of growths or limited levels. While not my favourite story, I really enjoyed Cindered Shadows, in large part because battalions were individual-specific and you had to carefully strategize over who to use based on their overall utility.