Recording in mono severely limits the waveform - why?

Please confirm if it is “limiting” at “-0.5 dB” or “0.5” on the vertical track scale (0.5 linear).
0.5 dB is only a tiny fraction below full track height, whereas 0.5 on the linear scale is half the track height.

Assuming that you actually mean “0.5 linear scale”:
In the Windows Sounds settings, Recording tab, is the Focusrite set to record “1 channel (mono)” or “2 channels (stereo)”?
(Windows 10 often sets this to mono, even for stereo USB recording devices, requiring the user to manually change it to stereo).

It should probably be set to “2 channels (stereo)” because the Focusrite Scarlett 2i2 is a true 2 channel device, even if you are recording only the first channel.