The issue is not that the theatrical version is simply shorter. What matters is that important, actual characters (e.g. Thrain) were dropped from the Theatrical cut because for some reason we required the creation of a new character in a literary universe that literally contains hundreds of characters, and at least dozens which are directly relevant just to The Hobbit and the events surrounding it. We didn't need to create more characters for an adaptation to be successful, and Galadriel is already an incredibly strong female presence who will likely have her chance to shine in the third Hobbit film, should Jackson and co. try to stick somewhat to the events of the universe they are adapting.
It's just baffling to accept weaker character development for ACTUAL, NOVELIZED characters in favor of creating a character that never existed in the first place, that completely ignores the rules of her universe and uses magic that was previously reserved for basically the most capable healing elf in existence (Elrond). There was absolutely zero need for Tauriel to exist beyond, at most, the jail cells of Mirkwood (just so we get the spiel from Kili about his promise to his mom, how nice), if at all.
Legolas could still have:
Captured the dwarves.
Talked to his father.
Questioned his father's motives.
Had more dialogue with Gloin, Gimli's father.
Chased after the dwarves after their escape.
Saved the young girls from Bolg.
Chased after Bolg.
Kili could still have:
Had a spiel about his mum at some point, even if only with a fellow Dwarvish prisoner.
Been injured (just not with a Morgul weapon, because lowly orcs should not have such powerful weapons flying around mid-air).
Helped protect the girls despite his injuries (y'know, to
[Show spoiler]make his death next movie more sad and all
).
Received some actual dwarvish/human healing, without retconning Fellowship of the Ring. Maybe he could have even gone to the mountain with his kin, or even if not, it still would have been just as emotional for him to be left behind.
Participated in the next film, without defying the laws of the established universe.
So no, not necessary. Not in the least.