If space and viewing range is that limited, how are some of the larger mechs in the RP even supposed to fire their weapons let alone acquire targets? They'd be just as limited as wheeled or tracked vehicle would be. I see them having to wade over hills and awkwardly maneuvering themselves into firing positions while under fire. It would be...messy, to say the least. 

Sounds like an environment where soldiers in powered armor, exoskeletons or battle armor (like the Elemental from the Battletech universe or the Terminator from the Warhammer 40k universe) would excel in---not vehicles of any kind, since so many hills, ditches and other hiding places would allow plenty of opportunity for a soldier using heavy weapons (like an anti-tank/anti-mech missile launcher, anti-material rifle or even a well-placed explosive charge) to effectively and efficiently down a larger target with little risk involved.