When i first fought lystrix, i was over paranoid about how strong she'd be, so i bred and tamed 5 spinos, and 5 rexes. It was an absolute pain to get them to an obelisk, but when it came to the battle, it only lasted around 5-7 seconds. Might have been my settings, might have been my choice of dinos.
I went in with two Daeodons eight megatheriums a yutyrannus and one megalania to kill the alpha version. I climbed to the ceiling of the cave with the megalania and blasted it with rockets from the roof while the megatherium tanked it and the yuty gave the Megas a buff and the daeodon healed