Space is extremely large and mostly empty. People tend to misunderstand Kessler syndrome a lot because they build their idea on faulty representations. For example, if you go to the wikipedia article on Kessler syndrome, you will see an image where centimeters long debris are symbolised by kilometers wide dots.

> This might effectively lock use of Earth orbit away for centuries.

It would make exiting earth orbit and placing an object there significantly more complicated because you would need to take into account debris, probably detect them from the object and manoeuvre a lot more but it wouldn't entirely lock up use of Earth orbit. It would also be a solvable situation. Cleaning debris is doable.