It's annoying (and ignorant) author lumps aircraft & boats into 1 category.

Jumbo jets won't be electrified anytime soon. Weight (and thus, energy density/kg) is everything. But synthetic fuels, hydrogen etc might be good options.

But there's also short-haul flights. Routes with say, 15..20min between take-off & landing. For such flights, electric aircraft is entirely feasible. And being done (successfully) in some places. Not to mention eg. training aircraft.

Boats: veeerry different. Weight isn't a biggie, neither is volume. And there's short-haul ferries, long(er)-haul ferries, cruise ships, 10000+ container giants, tug boats, recreational boats that hardly ever leave lakes/canals/rivers, sailboats with engine that's mostly used while entering/leaving port but not out @ sea, etc etc.

Each of these have their own economics. Where they're used and (energy) infrastructure there, is also a factor. Container giant on Asia-Europe route? Good luck electrifying that. Small tourist boat doing 20..30km/day in a natural park? Electric is a no-brainer, today.

And there's existing vessels vs. newly built ones. Most boats get old (like aircraft), more so than cars. Retrofits can be difficult/expensive. But for yet-to-build boats, different story.

Lumping that all in 1 aircraft/boat category, and claiming "uneconomical!" is just dumb.