Fission lacks commercial viability in large measure due to extreme, overly burdensome regulatory regimes that require dramatic overbuilding for safety margins,

Fission lacks commercial viability in large measure due to extreme, overly burdensome regulatory regimes that require dramatic overbuilding for safety margins, high barriers to adopting potentially-cheaper but architecturally novel designs (basically anything other than pressurized water reactors), and years and years of capital-cost-incurring red tape to deal with compliance. I think on paper, you're right that fission ought to be more commercially viable than anything any of the fusion people will be able to achieve any time soon, but I think there's at least a chance that fusion technologies will manage to get themselves regulated in a way that makes the all-in costs of fusion projects much more manageable, even if the reactor itself is more expensive, less power-dense, etc. In an NRC roundtable discussion last week, there was discussion suggesting that much of the need for, say, handling tritium, could be regulated under existing, relatively lightweight regulatory structures already in place for things like nuclear medicine waste, and it seems like both the US and UK energy regulatory authorities are pretty interested in building streamlined regulatory structures that make fusion much more approachable than fission historically has been.