Khmer Ability is bad?

question about khmer: if i build a building on a river, it doesnt "remove natural yield of tile". that means taht normalyl it does. e.g. theres a river with farms or fishing boats that gives 2 food or whatever, if i build a building there, that 2 food goes away. but with khmer it doesnt. got it. but after the antiquity age, i have a new civ, and now those buildings DO block that natural yield, right? so long term, if i'm focusing on getting buffs to river yields, and then i build over them as khmer, but in teh next age i wont get any of those buffs/river yields...right?

that seems like a bad ability after the antiquity age, since it means i'm poorly planning my cities.