Some interesting takes in this thread.
Anyway, cool that they managed to breakeven, but as was mentioned it took a whole lot of external power to focus 2.1 MJ (return was 3.1 MJ), (by the way, mega is M, milli is m).
The biggest thing you need to remember is the type of fusion device -- the breakthrough occurred with inertial confinement fusion, where lasers are focused into a tiny area and compress a ball of fuel, causing fusion (the real answer takes longer to type out and I'm on a short break). How is that scaled up to production? Giant lasers on a giant ball of fuel? That answer is unknown and will take time to figure out.
The other type of fusion is the magnetic confinement, which is probably most well known. The Tokamak style of device uses high magnetic fields to contain a plasma, which is approximately 200 million Kelvin. That's the ITER plant, being built right now. Their theoretical return is 10x the input, which would be really cool. The thought is that the size of the thing (which is massive compared to any other fusion test device) may help with that.
There's also the even more pressing challenge of materials. Just imagine: you have a superheated, 200 million K plasma about a foot away from supercooled, superconducting magnets, which are around 4 K, separated by a magnetic field and some steel. The material degradation is immense, thermophysical stresses are incredible, and that's not even counting the particle flux from the plasma, the damage it causes to the structure (neutron and ion bombardment displace the atomic lattice and cause embrittlement among a host of other phenomena).
The good news is that yeah, fusion is still probably 50-100 years away, so we have some time to solve the material problems. If you take anything away from my response, it should be this: materials are always the weakest point, even moreso than physics and mathematics. I do hope that fusion becomes a reality, it might happen when I'm near death or dead -- hoping the world is around long enough for that to happen.
As an aside, it was an interesting point about AI help -- that might be more promising than I think. For now, we'll keep working on materials research to help stand up to these extreme environments. I'm hoping the next couple fission reactors built will help restore some confidence in the nuclear field, they are a great stopgap against fossil fuels, when combined correctly.
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