They were defiantly off guard, yes. It actually depends on the individual Jedi. Some are better than others. Against a surprise of that magnitude it wasn't as good because they had completely let their guard down (after all, they were fighting along side with these same clones for 3 years, then outta the blue, they clones gang bang them) and weren't reading the clones mind for suspicious behavior and they were facing the other way.
i dont mean precog as in ability to see distant events or anything like that. combat precog, a jedi sees things before they happen, like anakin with his pod racing. thats why that seem to have such great reflexes. so does their ability to see what danger is comming in the moment, beat spidermans. if they were both being shot at would the spidersense or the jedi precog see where the shot was heading pick it up first.
also i think spider-man could take an average jedi in combat, he wouldnt try and go head to head and a jedi has no real ranged attacks other than force push, or throwing an object at him. hed wear them down and a nice 10 ton punch would take them down. someone like yoda or anakin would probably take him down though.