China dwarfs Mongolia: about 9,371,225 km² km² against 1,560,428 km² km². At true size China is about 6× larger — the whole of Mongolia fits into China roughly 6 times.
Both sit in Asia, so this is a same-region comparison: the new Equal Earth map draws both with the same honest geometry, and the real gap is exactly the 6× you see above.
The old map muddied it further: Mercator inflates China about 1.6× and Mongolia about 2.2×, so on a Mercator-style map this pair appears 4.4× apart instead of the true 6×.
Mongolia fits 6× into China.