Modern ones feel totally fine at highway speeds. We have a 2017 CVT Suzuki Spacia and it feels totally safe (not wandering steering or vibrations or anything), normal, brakes still stop it quickly, and the engine is not strained on the highway at 120 km/h (of course the crash safety of these things is terrible due to the lack of crumple zones so you should not drive at that speed, but it feels totally fine, to the point where I've accidentally started speeding without noticing)
The loaners we've had during shaken are all like 10+ years old and terrible, just as you describe.
How is the Spacia if you splash through a bit of a puddle on the highway?
Does the wheel jerk, bump steer a ton at that speed?
If you happen to have noticed, how does it handle something like a steel plate (temporarily placed during road work) ?
I have just recently found out about the Subaru Sambar / Daihatsu HiMax microvans and have been very curious. Since I'm unlikely to find an opportunity to test drive a Sambar, I was imagining that these little citycars might be a bit unstable at higher speeds, wet conditions or travelling alongside semi-trailers on CONUS State roads and certainly the Interstate.
The loaners we've had during shaken are all like 10+ years old and terrible, just as you describe.