Yeah, the decision to have junction tables for any kind of relation that came with the v4 was too a bummer.
Because of this new constraint I had to go back to the whiteboard to re-think my models. Because I relied on “unique” property for some one-to-one or one-to-many relation attributes to ensure no duplicates for some tables.
But with all relations now being done via junction tables, they removed the “unique” checkbox from the Content Builder UI 
because you can’t easily do it any more with the new architecture.
So, when I discover that, I thought, “F*ck I am screwed, what’s left? Transactions? Well, it is a heavy hammer but do I have a choice?”
Ironically, I then discovered that there were no transactions too and that’s when I started sweating 