This type of fold - Is the strength all in the hinge? (pics inside)
 

https://imgur.com/a/8XZg1

From what I can tell, the hinge seems to be the only thing thing holding together. The latch is plastic and doesn't do much and when there fold comes nicely together, it doesn't seem to be forming anything structural. Is this assessment correct?

If so, how strong is it?

The hinge will provide most of the vertical stability.
Since one half sits inside when closed, that can deal with torsion, If the fit is tight enough.
How strong the clamp is is an impossible question w/o knowing exact proportions, materials, degree of preload etc.

adequate in normal use ..

Thanks for the responses. I'm just wondering why there are holes in the flat pieces, but they're not actually joining to create anything stronger, and why the latch side doesn't seem to be adding any strength, like the Brompton does with the twist screw.

With all this talk about about frame hinge failure, it makes me think.

The latched looks like die-cast aluminium to me but if plastic, hopefully it's a tough glass-filled version.

The clamp gets it strength from the flange on one side going over the flange on the other side. It is held tight by the clamp but the flanges appear to be a force fit together. I would bet it ends up being quite strong.

Generally these hinges are well engineered and outlast the welds on either side.

If you look at failures of frames of this kind, they tend you fail at the hinge, but not the hinge itself.