In Waterman you solve the first layer minus the DF edge. So Waterman CLL ignores the E-slice and the DF edge. Advanced Roux solvers use multiple CMLL algorithms to modify the edge orientation during corner solving to avoid 6-flips. Waterman himself near the end of his 'career' would inject M/M' and/or convert r to R during CLL, to solve a U-layer edge at the same time as solving the corners. So Waterman CLL is actually a lot deeper than just CELL.