Its free to include, it stops shenanigans, it comes in untapped, and it taps for mana
Creatures have been around Magic since the very beginning, while saga is an enchantment subtype introduced in Dominaria
For decades, we'd had the block model, which always tied them together, but since we'd stopped doing it, the sense of a Magic year has started to drift away (except for the shared rotation)
The problem is very little of it has any basis in Magics multiverse, so feels less like Magic-does-manga and more Magic-does-Yu-Gi-Oh
No boring templates Start from an idea, then make it completely yours
Sacrifice outlets are also too diverse in their function to be easily switched off by a single counter card unless its incredibly specific (Angel of Jubilation or Yasharn, Implacable Earth come to mind)