You would still want to use remote manipulators even if you can open the reactor. The problem is not "small ports", it's that parts of the reactor vessel itself

You would still want to use remote manipulators even if you can open the reactor. The problem is not "small ports", it's that parts of the reactor vessel itself become irradiated. People can and have easily fit through the ports on JET, and will be able to on ITER. The remote manipulators are an amazing piece of technology; having the movements of your arms and hands replicated exactly by a robot is mind-blowing.