You're talking as if fielding a second XI will make defeat a fait accompli; it won't. Carlo needs more than 11 players to rely on this season, if we are indeed to challenge on multiple fronts. Early stages of cup competitions are pretty much the only time you can rotate to any great extent, while facing little risk.
Of course, it COULD blow up on us, but then as you've already said our first XI could suffer a shock defeat, or win but pick up injuries/niggles.
We all want to progress, and to win trophies. Me personally, I'd rather be through to the next round, with some fringe players giving Carlo something (positive) to think about, and our best players rested and ready to go, to trounce the Baggies at the weekend.