EC even on story mode requires more coordination then the other two ops so trying to PUG it would be messy.
KP is already a massive chore doing it with a pug thanks to the Towers of Hanoi. It's gonna get a bit better with the removal of the proximity mines on Story Mode come 1.4, but, even so, teaching someone that doesn't know the puzzle already can be outrageously frustrating.
The only Ops I don't mind doing with complete pugs (re: haven't been at least minimally vetted before joining) is EV since, honestly, the strats are relatively simple and the puzzle can be solved and taught incredibly easily. Personally, I *love* the fact that the developers have provided a puzzle boss with each ops, but, honestly, it cripples the ability to run with complete randoms. If the game had integrated voice chat within Ops and groups, it wouldn't be that bad, but, any fights that require a substantial degree of coordination and strategy aren't really gonna happen when you're dealing with 7 people that you've never met and some of which are likely to have never seen the content ever before, much less researched it so that they're understand the basics.