I really don't think it's as easy as that. Of course there are others but identifying them and persuading them to come to LFC may not be as easy as it sounds.
We haven't signed one player who can be described as absolute top quality and at the height of their game (maybe Sanchez would have been in that bracket had we signed him). Salah and Mane have been revelations but few saw them as 'galacticos' (to coin a phrase, however inapt) before they arrived.
However as far as that goes re. CBs then take a look at the 'recent' transfer activity of City, United, Arsenal and Chelsea with regard to CBs ...... Rudiger, Luiz, Otamendi, Mangala, Lindelof, D.Sanchez are their most recent CB signings ..... and not one can be called top notch (and maybe not even better than we have) whist most can't even establish a regular starting slot. Maybe Christensen at Chelsea is the nearest to a successful CB signing .. but he was theirs anyway and just recalled from loan.
Hence the interest in VVD, he should be superior to any of that lot and is experienced in the PL and against aggressive , physical, forwards (SPL). As well as for a team that spends most of the game on the attack (Celtic) playing with a high line.
There will be other top quality options but few could be considered objective targets and of other not so highly rated or experienced maybe we'd end up in the same situation as those listed above - there are no guarantees.