Rarely, and mostly against IG thanks to Wraithguard being pretty awesome vs them, but Faction Wars are not a great place to assess balance. well atleast they usually involve some of the best players and you have an isolated battle of one race against the other. I guess the fact that they are 3v3 is...

fire Prisms are undertuned imo, felt this way since like ever, especially compared to the leman russ, the other tanks are somewhat fine due to the significantly lower range. the whole eldar race is so micro heavy and kinda doesnt reward you enough for it if you do it well, too bad the playerbase is ...