Just to sum things up, I had an unexpected chance to test a 1x8 setup this morning.
Although it wasn’t the Microshift Sword but rather an old Shimano something, it had the gearing I was looking for (38t with 12–42t).

On the drive lane, I easily reached the 7th gear on flat terrain with a tailwind, and the 8th on short slopes (about 150 m long). This makes me think that on longer slopes, I’d probably run out of gears.
It convinced me that, for my riding style and on a gravel bike with a more aggressive/racing position than the one I tested, the 1x8 would feel limited.

This basically confirms what most of you have been saying: it’s a personal choice, but if you tend to push more on the road, the 1x10 is probably the best balance to have.