Definitely true, and they had other positions where they lacked good enough options in most other positions. No other CB at the quality of van Dijk is normal, but probably no natural fitting cover at full back either. Midfield was the only area they had real quality cover along with whoever partnered van Dijk.
They got away with it, but probably had to get a bit lucky with injuries and have done strengthened for that reason.
We can cope without adequate cover in the front three, if we're lucky with injuries. But right now we lack good enough options in most positions. Arguably only central midfield (Bentancur, Hojbjerg and Skipp) as well as LWB where we're not massively weakened by a single player being out. That's too much.