to be fair, they are at the mercy of how they are mixed by the engineer
The levels aren’t usually as much of a problem as eq/effects/etc. You set up a lead vocal very differently than a backing vocal. For things like Natural and WWY, you want both vocals treated more or less the same way. Whereas when Mark or Liam or whoever take those parts, their mics are in backing mode, eq’d and reverb’d to blend in and avoid stepping on the lead vocal, and CH engineers have generally not opted to try and recalibrate that on the fly mid-show.