Why are NPC parties so bad?

[Thangil]

I did Grand Cosmos the first time with NPCs and it went well enough. Slow, as expected, but got the job done.

Think the system is perfect where it is? Less efficient than playing with players, which is good because it encourages you to play with others instead.

Then you didn't have the issue I had, where Alphinaud got one-shotted all the time.

[Astronis]

I will admit I have laughed myself silly when Alphinaud has stood in tankbusters, Estinien pulls packs ahead of me like a proper greedy dragoon, or when two certain guest NPCs both triggered their Limit Break at the same time but one was a hair faster. Generally, my experience has been that Alphinaud and Urianger are very competent healers and can heal me through all kinds of tank shenanigans...though neither of them seem to recognize how Living Dead works. I went into the Aetherfont as a Gladiator once for giggles and Urianger still managed while I pulled everything, though I had to do a lot of work on my end too.

Buuuuut...yeah, they do dumb stuff too. In the Grand Cosmos specifically, I watched Alisaie head for the same stuff I was to transfer the mortal flame but I reached it first, so...she just kind of ran around screaming until she died. In Babil, on the last stretch before the last boss, ALL OF THEM will stand in every AoE they can find. They aren't optimal companions.