To avoid people from feeling like they had to pull hundreds of packs of a reprint set before the deadline to get these rewards, the game counts all prior versions of the necessary cards for them
On the other hand, when going second, the deck can blitz an opponent with high early damage incomparable to most others, facilitating a major offensive before an opponent can prepare
It's a 2-cost instant that can give all stuff -1/-1 (unlikely here), destroy an enchantment (possible), or save your team (probable)
The turn after we cast our Starfield of Nyx, we reanimate History of Benalia for free and get two 2/2 Knights (one on our upkeep, one after our draw step)
The reason this kind of card isn't used so much these days is that even if you get the god opener with a turn two Reanimate, Exhume etc you will still often lose the race if you do nothing else, particularly if you pay 8 life