I should have made it clearer, you don't always keep your centre of gravity low, just when you see a sweep coming in for your feet. Even if they change their aim and hit your knees, you should be ok. Just sink down then do your counter. Don't be a static target. Judo guys love that.
I've never done randori with a judoka who could knock my legs out by hitting my knee with a sweep or a jujutsu style 'leg plant' once I knew they were going to sweep.
Guys who get you by surprise though.. different story.. watch out for them
But then judo works best when opponent is surprised.
Ever notice when you try to do a technique and the opponent resist, but with a sudden change in technique you can easily throw your opponent? This works because your opponent is taken by surprise. IMO surprise is what make jujutsu'esque technique work.
Knowing one technique that will surely work is better than knowing hundred that will probably work.