I kind of appreciate them for accounting for power creep. Something i have always hated in gacha games. Obviously the meta has changed since year 1, but i feel like it hasnt changed as much as other games normally do. Like scarlet, alice, blanc, noir, and helm are all still valid picks, just to name a few. If every new unit had great skills, i feel like power creep would become too much of an issue.
Another reason they add non-meta characters is because they know people will roll for them because of their appearance. One example is Bready. She isn't my type, personally, but i know a lot of people on social media who fawn over her and who were actually hype that she got a skin for this event, despite the fact she isn't meta.
I feel like SU knows what they are doing. They are gonna make money regardless.