Gotta love anything by/from Mike Judge and that Lomborg is basically a character out of Idiocracy.

That said, corn is more efficient because it's a kind of grass (carbon refixation). Rather than more trees, it's worth considering more prairie grasses that per-acre sequester more carbon - and that sequestration is in the root systems so it is less likely to 'go up in smoke'.

Back to photosynthesis. A lot of our planet's CO2 conversion is in algae. Photosynthesis in those becomes less efficient as acidity goes up - and the higher atmospheric CO2 is diffusing into the oceans, shifting Ph in that direction. Some algae varieties are less susceptible (CAM - essentially breath holding through the day while other algae are acidifying water, then exchanging gasses at night). This adaptation also conserves water, so some land plants adapted for aridity also do this (e.g. bromeliads).

TC;DR: it's complicated, but yeah, no on Lomborg's idea.

Not a botanist this is mostly what I remember from HS biology class. I was lucky enough to have a teacher who had done research on corn in the 60s and I was that irritating smart kid in science class (sorry!).