Even before as well technically. Part of the reason for gain staging properly is to make sure you provide appropriate signal level to all the various inputs stages. It is a holdover from analog, but still applies in Digital, even in floating point systems with enough headroom to handle it to an extent. For one thing just because Ardour uses interally 32 bit floating point math, doesn’t mean that the plugins handle it all the same. Related to this though is that most plugins provide control ranges based off a sensible level incoming to the plugin, and if you overdrive the plugin (Or underdrive) you may find it very difficult to manipulate the audio using the plugin controls like you might like.
So in general it is a better option to lower the input levels, but can you get by in most cases lowering the master fader? Yes, but not in all.