Vanishing Vanishing offers a two-sided effect
This said, both cards are currently banned in Legacy, and they are both brokenly powerful on their face, so my guess would be that they were simply too good for Standard, rather than being part of a specific oppressive combo
Friday Night I went on to 11 straight losses
An enters ability is super easy to breakimagine a Krang, a Displacer Kitten, and a ton of 0-mana artifacts
Similarly, any of the other Soul Sisters like Essence Warden, Soul's Attendant, or Prosperous Innkeeper work instead of Soul Warden
When 70% of instants and sorceries in my cube are 1 or 2 mana and the average CMC of such cards is about 2.5 (realistically a lot lower as so many of the high cost cards have delve or pitch and alternate costs) you start to appreciate how good four mana and higher spells must be