Fusion reactors are more complex in every possible way than fission reactors because of the sheer temperature differentials (super cool magnets next to hot neutron blanket).
Plus, they have much more parasitic power loss (running the superconducting magnets and cooling them to keep them superconducting, plus keeping the vaccum in the reactor chamber all require massive power, and they scale with the size of the reactor). You need some extra power to produce hydrogen through electrolysis as well, though that is probably lower. Note that making the magnets stronger to keep the vessel lower (so that everything is more easily cooled) will not get you much more, since we are already nearing the limits of material resistance for the supporting steel structures in the presence of the extreme magnetic forces trying to crush the reactor together - especially given embrittlement.
Not to mention, you will always need at least a small fission reactor to breed some tritium, since the fusion reactor will always have some losses.
Finally, the much much higher neutron flux that fusion expels (32x or more neutrons, and much higher energy per neutron as well) means that everything close to the reactor becomes brittle in 2-4 years. This means that things like support beams and the magnets themselves need to be constantly replaced. Even worse, they become medium level radioactive waste, which needs to be stored.
These are all intrinsic limitations of fusion that fission reactors just don't have.
Plus, they have much more parasitic power loss (running the superconducting magnets and cooling them to keep them superconducting, plus keeping the vaccum in the reactor chamber all require massive power, and they scale with the size of the reactor). You need some extra power to produce hydrogen through electrolysis as well, though that is probably lower. Note that making the magnets stronger to keep the vessel lower (so that everything is more easily cooled) will not get you much more, since we are already nearing the limits of material resistance for the supporting steel structures in the presence of the extreme magnetic forces trying to crush the reactor together - especially given embrittlement.
Not to mention, you will always need at least a small fission reactor to breed some tritium, since the fusion reactor will always have some losses.
Finally, the much much higher neutron flux that fusion expels (32x or more neutrons, and much higher energy per neutron as well) means that everything close to the reactor becomes brittle in 2-4 years. This means that things like support beams and the magnets themselves need to be constantly replaced. Even worse, they become medium level radioactive waste, which needs to be stored.
These are all intrinsic limitations of fusion that fission reactors just don't have.