Tbh it's hard to judge the defenders under Mourinho-ball and with Sissoko/Ndombelly/Winks for 'protection'.
I know it's early days but the addition of Skipp to complement PEH has really transformed how solid we are. Dele's running has helped with this too.
I wouldn't be prioritising a CB for now. The time to upgrade at LCB is next summer but for this season Romero plus one other behind a very solid midfield is sufficient.
It is way tooooo simplistic to blame other aspects.
Specially if mistakes are made player against player defending. Again, like the infamous Sanchez vs Gundogan situation. However much you stretch it, you can't blame manager.
You can't blame manager if defender goes to head clear the cross and just misses the ball...
Sure, now we look more solid, but I pointed it out - it comes at significant cost - if we play 3 CDMs whos main aim is to keep our fragile defense not being troubled, it will make it lot harder to unlock defenses, specially if opposite team parks the bus.
Playing 3 CDMs just masks the defensive issues but does not solve them.
Of course I hope that Romero becomes commanding CB and someone (Sanchez, Rodon, Dier) becomes reliable partner for him in CB positions. But up to now Dier and Sanchez with all their errors have made me sceptic about this happening.
Let's face it - after last season everyone agreed that defense and more specifically CB area is very big issue for us. And in summer we moved Alderweireld out, Romero in. This is just upgrade on one player there. I feel that current run of 3 clean sheets makes people over confident about our CB levels.