To note, Olivie's benefits are more than her team wide buff to elven units. Because of her skill she becomes a full on dodge tank if you devote to her skill lvling, which means if the threat of the map has physical damage as its attack Olivie will laugh her ass off while she's slicing into it with her 900 attack power swings (I say 900 because of Olivie's stats at lv 80 that are then boosted by the Big Hero Prince title.) Plus since her elf buff affects her as well, she gets a free point chipped off her cost in addition to being given extra MR.
Sherry is a two-fold benefit. On one hand is whenever Skill AWing comes out. While it does take investment, once she's prepped for the second skill use its almost like having 5 Sybillas in one spot. Without it however, there is still a reason for her to sit in the team for her AW buff. While its only a stat buff for Golds and lower, its the main composition for most freemium players is usually golds and silvers so having her in the premium rolls is like a blessing for them.
Anya is a part of the Specialty Princess Coalition. In her case, you have a Princess with no natural MR until she gets AWed but has a skill that cuts all physical damage taken by half and has a block count of 2.