While it is better to pay the one mana most of the time, sometimes you just can't if you want to make any kind of progress on your board state
The reason its come in as high as it has is because of the potential it has
What affects the value of Obsessive Search
From the pre-game discussion about power levels or possible strategies to acclimatize everyone to each other's decks to making sure one's deck doesn't monopolize time at the table, these "rules" are in place to make sure everyone has a good time
That top creature has all abilities of the creatures underneath it, plus its own abilities
There are certainly some themes present in this expansion, but because of the sixteen games in the series, it feels like the cards are all designed to do various weird and unique things, at the cost of them being rather weak in power level