Mell lost at least 2 fights, Harrison and the first Castano fight. He may have lost to Martirosyan as well, but it was close. He definitely got the A- side treatment in that fight. I give Mell credit for winning his rematches though, and the Castano win is his best by far.
Apparently you forgot that Mall beat Derevyanchenko who is miles better and tougher than Harrison. Derevyanchenko would chew up and spit out Harrison. I think Derevyanchenko may have beat Castano in their world series of boxing thriller as well, but the fight was close and in Argentina. Such a classic.
I think Mall is more of a classic boxer behind a outstanding powerful jab. His best win is an uncontroversial win over Derevyanchenko which was impressive. I think Mall is the more powerful Charlo as well. I rate Mell slightly less talented but more tenacious, and more of a risk taker than Mall. He seems to be a harder worker than Mall. His only apponent i consider on the level of Derevyanchenko is Castano. So with hard work and dedication he proved he was able to beat someone at that level, after clearly losing the first one, then getting the uncle Al rescue treatment in the first fight.
I had them about the same level but now I have Jermello ahead cause he's been active unlike his brother and in that period he became undisputed at 154. I also really liked his performance in the second Castano tight I thought he looked pretty good in that one.