Sacrifice removal effects tend to be the perfect answer against control or midrange decks playing few creatures, and Invoke Despair tacks on even more value by netting you cards and dealing damage through life loss
It feels like being caught in a rubberband - players get thrown back after moving forward, making it look like your character teleported or warped from one place to another
In Solphim's case, this requires you to discard cards in addition to the other costs
Switching to Shalai and Hallar means that in the 99, Keen Sense and Snake Umbra can draw us a ton of cards, and Chandra's Incinerator becomes repeatable removal at a super efficient rate
At the same time, it won't gain you life either the way Savra will, but since lifegain is negligible...yeah
Hard counters are very powerful against Ramp for this reason