The issue with partial success is ... is the partial success just random bad luck?
I have no problem with PCs "losing" if they make a bad decision. But unlike real life I prefer not to have things go sideways if it was simply out of ignorance, if that ignorance was not caused by truly poor judgement. In other words if they didn't track down the 3rd McGuffin because of bad luck, die rolls or simply inadequate hints provided by the mod then the PCs not being the heroes they mean to be leaves a sour tasted in my mouth.
Which doesn't mean bad things don't happen in my campaign. They do all the time. But the players can always look at Bob and say "This happened because you didn't believe us when we told you that the warlock Bad Evil Guy needed to be stopped and you let him go!" Actions or lack of actions have far reaching consequences, simple bad luck they could not have avoided can also have negative outcomes but I avoid the world-breaking cataclysmically bad outcomes because they didn't know they had missed anything.