We haven't looked solid defensively even with our first choice defence available. We've conceded 14 goals in our last 6 matches, for example. Romero, VDV, Porro and Udogie all look completely clueless.
As to Pochettino there were significant periods where he had to do without key defenders. For example, there was a run in 2016/17 where he was hit by key injuries:
Emirates Marketing Project 2 v 2 Spurs (defence: Vorm, Wimmer, Alderweireld, Dier)
Sunderland 0 v 0 Spurs (Vorm, Rose, Dier, Alderweireld, Walker)
Spurs 1 v 0 Middlesbrough (Lloris, Walker, Alderweireld, Dier, Davies)