According to Osho, witnessing is emphasized because it brings peace, dissolves mind and ego, and reveals nonduality—God/Truth—while concentration merely gathers mental energy, strengthens the ego, and keeps subject–object duality intact. Peace naturally yields authentic power; power does not ensure peace. Witnessing is both the path and the goal; concentration, at best, is a preliminary tool and can mislead if clung to.
Watching your thoughts without trying to control them makes you truly calm and whole, while intense focusing only makes your mind and ego stronger.