In my opinion Jirachi Has enough checks in the format to be balanced. For instance, it's weak to spread moves like Earthquake and Heat Wave, on its own it can't touch steel or fire types with Aegislash, Heatran and Volcanion able to hit it super effective.
Jirachi is however very good at letting mons like Kangaskhan and Diancie and have "free" hits through redirection - although still vulnerable through spread moves - and can give Azumarill a "free" Belly Drum. Personally, I think spread moves, Intimidate support and having a mon like Aegislash that can wall Jirachi makes Jirachi + Kangaskhan / Diancie fine to deal with and those things should probably be on most teams anyway. Also, although Jirachi + Azumarill is really good I think things like Quick Guard Talonflame could become more popular to help deal with it, on top of mons like Volcanion.
Finally, just in my opinion, Jirachi helps team-building more than it hinders it as it provides a nice check to Kangaskhan, Diancie and Amoonguss in one mon as well as providing speed control and flinch potential. Other re-directors just are not as good at doing all of these as Clefable doesn't handle Kangaskhan as well and Amoonguss is weak to Talonflame and Rage Powder doesn't re-direct through Safety Goggles and against grass types (although Amoonguss is better than Jirachi in some Trick Room teams). Overall, I think that Jirachi and its main beneficiary's are not too big a problem and with Jirachi gone things like Kangaskhan + Breloom/ Amoonguss will be more of a problem.
I really don't feel like I've seen enough of Jirachi. I saw it probably a maximum of five times during the suspect, and through talking with others & watching matches I still don't feel a strong opinion either way.