Nicrosil compounding was pretty much my theory too. Although TLR is also confirmed to be a savant in pretty much every metal. So in terms of power we're talking he's at least Elend's strength, plus the possibility of a strength upgrade from the well, plus possibly having ingested more than one bead of Larasium, PLUS being a savant. These combinations reasonably put him at the power level to achieve the things we saw him do.
(Although I still think Kel could have put up a better fight)