Adding another fader and another channel to clutter your project is only really smarter if you actually need it/use it.
If you don’t need to use these “many more possibilities” then you’re missing nothing and if you do you can easily route to group and drag the amp sim over when and if you need it.
Many plugins that aren’t made with special care for mono input, like modulation, delays, anything pretty much except guitar fx, you have a big chance of having routing issues like one channel comes out clean, or out of phase, or whatever, when inserting plugins of a different configuration of its track, so like its been done since the 60’s, we usually go for the most perfect setup, like using mono tracks for mono inputs and stereo tracks for stereo inputs…
I think you’re perhaps making a wrong assumption here…My thinking is that we don’t need to care at all about mono input as even though the file is mono it is already seen at the plugin input as stereo (or dual mono technically) because it’s on the stereo track.
If you can name any one of these plugs built with no care for mono input I’d love to confirm this.