As Marcello said, you can simulate large sand berms and similar by using terrain elevation. I generally go for this for fortified bases and the like. Real, urban-terrain walls are much harder to come by, as well as fences as a minor note. Ever tried to make a map of downtown Berlin pre-reunification?
Looks like you are mostly talking about lower human-scale berms here, right? Like ones used for low-level fortifications, e.g. around dug-in tanks?
If we consider infantry entrenchments, the game detail level is low enough you can assume that berms are implied in trenches and infantry caches, and that e.g. rough terrain is good enough for the rest.
Back to the point, the one place where I'd gladly see berms is indeed around buried tanks. Right now they get the same sandbag circle as crewed weapons, which I can understand from a game mechanics perspective, but if at all possible, I think some within-hex sand berms
like these for dug-in vehicles would be nice eye candy. Replace sand with earth and you have the summer variant.
For the smaller stuff, I don't think you can expect that level of detail in 50m hexes, and the larger stuff (aircraft shelters and base defenses) can be dealt with using elevation.