What a weird thing for someone to say.
Agents of shield is a big success, both quality and in terms of running for 6+ seasons.
Agent Carter got cancelled pretty fast, reasonable to say it was a failure.
Daredevil has excellent critical reception, 3rd season incoming, no sign of stopping, clear success.
Jessica Jones has solid critical reception, 3rd season incoming, no sign of stopping, clear success.
Luke Cage has good critical reception, every indication of more seasons to come, clear success.
Iron Fist did get a second season, but the first was pretty meh, wouldn't quibble with calling it a failure.
Defenders also perhaps fair to call a failure.
Punisher had controversial critical reception to some degree thanks to the subject matter, but pretty well liked, getting more seasons, etc. Pretty hard to spin as a failure.
Runaways and Cloak and Dagger are both getting second seasons, medium quality, not spectacular viewership but not disastrous either.
So maybe 3/10 MCU shows could be called failures, or 5/10 if you wanted to be really harsh and stretch things.
On the other hand, 0/0 DCEU TV shows are failures, so I guess you could try to spin that as a 100% success rate :p
Edit: LOL, also there's the one show so bad I'd completely wiped it from my mind, Inhumans. So 4/11.