For all the focus on Arsenal’s greatest strength before toSunday’s clash of the Premier League titans with Liverpool, Virgil van Dijk feels that there was also a weakness waiting to be exploited. And exploit it Arne Slot’s visitors certainly did. Arsenal may have topped the Premier League charts last season for set-piece goals – they are also leading the way this term with four – but to describe Mikel Arteta’s challengers as the masters of a dead-ball situation would be to ignore a rather crucial point. Only Southampton and Wolves, with seven apiece, have been breached more often outside of op…