Agree on both.
You need to also consider the lens construction. For example an old prime may not be better than modern zooms that uses new technology (multi-coating, low dispersion glass, aspherical elements, etc) The 18-200 uses more special glass (Sigma's SLD) than the 18-125. The 18-125 is only marginally sharper at 125 but if you need 200mm, you simply need a longer zoom. But if you do not need so much zoom, then yes, a shorter zoom like those 17-55 f2.8, etc, would give you much better image quality.