To be honest, Fusion reactor never was profitable in other games. In this game could be, because of max slots in a planet.
In your main planet you have 163, so if you build plant, you spend more slots than if you build fusion reactor, but you need also gas plant. But you get more energy. What is better?
In other games you have Solar Satellite, which give you power, between 15 and 50 according the temperature in your planet, so, a planet in position 1 get the max energy from Solar Satellite and less Gas, but a planet in position 15 get the max gas and the minimun power from Solar Satellite.
As a result of Solar Satellite, you dont need to improve a lot of your solar plant, maybe lvl 21 or 22 at maximum and you have around 500/400 satellites giving you the power which can be destroyed.
So in this game, COULD BE useful to build a fusion reactor, but i dont think so, even position 15 with around 130 slots, is a bad option. The best planets are between 4-6 and there the gas has a normal production.
If we enter in late game absolutly is a good option, but in early/mid game around 100k to 5kk of points is not good.
Then, i think they can add the Solar Satellite in this game to help the lack of power.
About the topic, as i said, plant > reactor in mid game. Even in late could be better the solar plant, only would be profitable if you have sometimes in position 15 a planet with 180 slots at maximum.