Balancing the Giratina Lady

No not Cynthia but can there please be a balance to it so when I'm in the middle of the run I don't get jumped by a Xerneas while I have no legendaries to speak of? (Or a rock/flying tyranitar that perfectly counters my team) that basically forces me to get lower levels and or change my entire team? Like I get not every event has to be beneficial to the player but some liency would be nice

(I specify those two BECAUSE I HAVE BOTH OF THEM ON THIS RUN)