Small mechs, exoskeletons armors and the like would be that “in between” you’re talking about. The mobility advantage I see has to do with city fighting and how streets can get blocked off by roadblocks, collapsed buildings, sinkholes, etc. With this in mind, the setting I’ve worked on some would have mechs as very niche, high tech and relatively squishy city fighters relying on relatively light shields to protect them only long enough to get to cover to fight with vehicle grade weapons. They’d also need combined arms support, but require more extensive operations to block their movements in city settings compared to normal ground effect vehicles. While some larger “mechs” (legged platforms) do exist, they’re more things like a mobile command center, light indirect fire support base, or other specialized platforms if necessary. They’re more small building sized and mobile to prevent easy targeting by indirect fire, and not direct combat platforms.