I mean, wouldn't it be the opposite? If moves like Destiny Bond or Perish Song are "boss killing strats," then the fact that most bosses are immune to those strats makes them pretty useless, no? Against 6-mon teams they're really not that strong, since they can either switch, or they're down to their last Pokemon, in which case it's not really necessary at that point 9 times out of 10. They're best use is against big, singular enemies. However, 90% of the big 1v6 fights see the moves rendered completely unusable.
Speaking from experience, I've probably clicked Perish Song on my Mismagius three times total, once to test it out, once as a mis-click, and the third time I used it the Pokemon went down before the timer even ran out.
Also, in general the Shield mechanic can feel likean attempt at adding artificial difficulty, and they don't particularly add much sense of accomplishment to the fight in the end. All the mechanic added to my battle against Kyogre in Valor Mountain was that I had to Toxic stall it for 20 turns or so instead of 12 turns (and since Kyogre outspeeds and OHKOs nearly everything in my box, that's not much of a difference). While I don't mind their use in the Rift fights, that's mostly because I've barely noticed them in the Rift fights, and even then the seemingly arbitrary restrictions on what does and doesn't work on them sometimes bugs me.
, i hope that you will have a great day 
