Does 'Umrah in Ramadan atone for major sins and make the pilgrim return as pure as the day his mother bore him, by analogy with Hajj?

Umrah in Ramadan is not equivalent to Hajj in every aspect. Scholars have unanimously agreed that it does not absolve one from the obligation of Hajj. The meaning of "equivalent to Hajj" is that it equals it in reward only, not in fulfilling the obligation of Hajj. This is similar to reciting Surat Al-Ikhlas, which is equivalent to one-third of the Quran in reward, not in fulfilling the recitation of one-third of the Quran. Hajj has a greater reward and recompense.