Building a Dyson swarm to collect all the energy output of a star would effectively be the biggest possible fusion reactor, so I think a civilisation that can build fusion reactors would still pursue collecting all of a stars energy.

Even if you used all of the available fusion fuel (deuterium/tritium and any other hypothetical possibilities) you would not get close to the power coming from the Sun. The Sun contains 99.8 % of the mass of the solar system, and most of that (73%) is hydrogen. As our energy needs rise we will inevitably need to capture more of the Sun's output to meet those needs.

Depends on how we can scale fusion power and how much hydrogen we can collect in space.

With what raw materials could a Dyson Sphere be built with? The Earth is so much smaller than the Sun, how could we possibly have enough of anything to surround the Sun with a Dyson Sphere?

A fusion reactor, like the ones you hear about in the news, is a device that fuses together special kinds of atoms of hydrogen called tritium. Those fusion reactors are only designed to fuse very small amounts of those atoms at any given time. For example, the excess energy generated by the recent National Ignition Facility, that recently made headlines, was 0.4 MJ. That's just enough to bring a water kettle to a boiling point.

Compare this to the amount of energy produced by the sun, which is 380 billion TJ per second. That's more than enough energy to instantly boil all the oceans on planet earth.

There's no type of foreseeable human technology that will ever produce more energy than a Dyson sphere. That's why the Dyson sphere is considered to be some holy grail of technology / energy production.

It changes everything, fusion power causes tremendous radio interference, so we will need to place a satellite repeater on the far side of the sun, to avoid the EM interference from fusion. Otherwise we won’t even be able to get A cell signal in this star system captain. I’m talking 0 bars sir!

I’m pretty sure Dyson spheres assume we have the tech to capture 100%of the power being produced but I could be misremembering. Also if we do end up colonizing the solar system, I believe our demand for energy would be too high for fusion reactors alone and Dyson spheres (on paper) would provide the best means to meet that demand.

I think it really comes down to the ability to harness the fundamental forces behind electromagnetism. Up until this point the dyson swarm/sphere theories were built on the Idea that a star is the most optimal and long lasting fusion reactor and thus harnessing the 'top tier' energy source of the universe would be the be all end all.

However I do think a species that is able to master and modify completely the fundamental forces behind what holds our spatial dimensions together, we will realize there is more energy around us than we can manage to use. Everything up until that point will be ways to harness said energy in rudimentary ways of converting this energy into heat.

This is just a random internet persons thoughts. Would love to further my knowledge

I mean, if you had a fusion generator that magically created one star's worth of energy on your desk you couldn't use it like that, since all the energy it made would eventually have to turn to heat (like, you might make pure electricity and not put out any heat, but if you used that electricity it would net out to the exact same temperature as the star would have been) . spreading out in a big circle around a star is the only way that makes sense to use that electricity.