It's a good point that design and manufacturing quality are an important component here.

I know the e-scooters used by Lime and Bird have seen a pretty quick iteration, and the models they have on the streets now are a lot better than the ones they had when they launched in my city just a few months ago.

In terms of in-between vehicles, I haven't seen too much yet. Our current street designs (at least in most of the US) make it really hard to operate a vehicle that is too small/slow to share the big & high speed lanes and intersections, but too large to move onto sidewalks or pedestrian spaces when you need to fill the gaps between safer/slower infrastructure.

You could look at what they drive around the retirement communities, seems to be a lot of designs that use a golf cart as a starting point.