Some items to consider from the video
1. short flights spend an large amount of energy simply having the engines running during taxi to/from the runway.
2. Take-off also consumes much more fuel than cruising.
3. 1 & 2 combine to push airlines to prefer larger & larger planes making longer trips when using fuel (it's how they're managing that 45.9 seat mile number - it get much worse for shorter trips).
4. They're already pushing the 400kwh/kg range for batteries (I believe he makes an offhand comment in the video that they're using 8 packs, with roughly the capacity/weight of 4 tesla battery packs - which would put their batteries in the ~4k lb range if we estimate by teslas pack weights. They are likely pushing to go lower than that. I think it's not crazy to consider they're targeting a production weight ~50% below your guess - in the high 3000s)
5. On top of fuel savings, one of his more compelling points is that maintenance on their engines will be much, much lower. Jet engines are expensive to service, maintain, and repair (thousands of parts, complicated designs, extreme operating conditions). Their motors are basically 450kg dc motors - it's a giant drone motor mounted on an airframe.
6. they seem to have quite a bit of interest from existing airlines (ex - united) so apparently this does seem compelling to them.
7. He quotes a $5 take-off cost in electrical power. Something like an Embraer ERJ-135 uses ~20 - 30 gallons of jet fuel for the same thing (~$100). If they target a plane that's doing very frequent takeoffs/landings, operating costs could be considerably lower, not just lower.
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Personally - I don't know if they'll make it work, but it's definitely an interesting play, with more real thought put into it than most attempts I've seen.