Originally Posted by
Ultimatecalibur
There is a difference between mechanics being difficult with pets and annoying/cheeseable/breaking with pets. Targetable pets led to the later rather than the former. Multiple consecutive Raidwides in high end fights would often kill Egis and Fairies due to Sustain being unable to keep up forcing resummons (which took 6s to cast then) which heavily impacted both SCH and SMN ability to do their jobs, Ramuh EX for a time did not require tanks to clear due to the Egi/Fairy mercy mitigation (added to help with the former problem) also applying to tankbusters, AoEs that required stacking to survive often ended up weaker than intended due to having 1 or 2 more targets than they were designed for, as targetable entities they caused rendering and targeting issues during large player gatherings such as World Boss FATEs and S-rank hunts, and the Turrets could break fights such as Ifrit EX if they managed to be placed in the wrong place and gained aggro. All of the above and more are why targetable pets are not worth the hassle for mainline jobs*.
*Limited Jobs such as Beastmaster or Puppetmaster having targetable pets wouldn't be as problematic as limited jobs can be allowed to break the game more.