I think also its both because the awkward carrying position increases the effect of the high weight.

The other advantage of the Brompton and identical clones (i.e. with 16"/ETRTO349 wheels and folding identically) is that its really small with as consequence that its much easier to take it with you everywhere and avoid to leave it unattended.

FYI, a shoulder strap, either attached to the frame or on a bicycle bag make transportation even easier, the bike bag + small folded size make that few people imagine that you are carrying a folding bicycle.

The Brompton was designed for use cases like yours. No other folding bike will do the job as well.