The article doesn't seem to consider non-conventional launch strategies. With things like Project Orion, mid-air launches (by either balloon or plane), and space elevators all being theoretically possible, it seems unlikely that any given civilization would never be able achieve spaceflight, given enough time.

It's my impression that ideas for carbon nanotube space elevators would just barely be able to theoretically support their weight, even for earth, so there might not be any way at all for a larger planet, and we might never be able to make a practical one except for a smaller body with no atmosphere.

Right? A balloon first stage seems like an obvious work-around...

Insert xkcd about how the difficulty in getting to orbit is speed not altitude.

This is all the more true about a larger planet than earth.

Sure, you might have a thicker atmosphere, but that's an additional challenge. Needing a balloon (if it made sense, I couldn't do the calculation) would be a reflection of the difficulty above and beyond the increased orbital velocity that is the basic problem.

Well sure, but the majority of your energy spent is fighting to get up to speed while in the atmosphere. A balloon or dirigible or some buoyancy play should be able to get you to a certain atmospheric density regardless of planetary gravity. That cuts the bottom off of the rocket equation pyramid and reduces drag immensely at your 'starting' point.

Of course we could: https://xkcd.com/1162/