Both the last times we have had a glaring weakness in the team(strength in depth) Pep has identified them and done the business mid-season(Laporte, G.Jesus).
I don't believe for a second that he doesn't see the need for a LB and CDM. I therefore assume that there is just not the money being made available and somewhat rightfully so. Pep must have been happy with the squad in the summer and chose to sign Mahrez, a luxury signing as it's probably our strongest area in terms of depth. He identified a CDM but put all his eggs in the Jorginho basket without a back-up option and then after missing out and at the time being happy with the rest of the squad has spent the money on luxury. I reckon had we not signed Mahrez we'd be seeing a De Jong/Ndombele/Someoneelse rocking up here in January.