Nuclear energy is limited to a little less than 1% of the energy release possible with antimatter, per mass.

The practical limit for nuclear energy is about 5 to 10 times less than that, because the theoretical limit corresponds to the transmutation of hydrogen into iron, coupled with the capture of the entire energy, which will not be achievable any time soon.

But there is an essential difference between nuclear energy and antimatter energy. Nuclear energy is stored in our environment and you just have to exploit it. Antimatter energy is a form of energy storage, so you need some other form of energy to make antimatter. The energy efficiency of making antimatter is many orders of magnitude worse than the factor of less than 100 that exists between nuclear energy and antimatter energy and the mass of the confinement device needed for storing antimatter is also orders of magnitude greater than the mass of the stored antimatter.

For now, there is absolutely no hope of ever using antimatter in practice for storing energy. Such a thing could be enabled only if some technologies that we cannot imagine would be invented.

Despite the great technological progress of the last couple of centuries, it is hard to say that there have been many inventions that have never been imagined before. After all, already 3 millennia ago the god Hephaestus did his metal smith work with the help of intelligent artificial robots.