Shea Theodore just returned for Vegas. They're going to be a handful for any team with that defensive core behind Eichel, Stone, Hertl, Karlsson, etc. (And I'm sure, if the Blues matched up against Vegas in Rd. 1, Barbashev and Saad would be extra pumped up to inflict some pain on their former employer).
But while Hanifin, McNabb, Theodore, Pietrangelo, Whitecloud & Hague is a very deep group, the Blues own d-line is a deep, talented & veteran group in their own right: Parayko, Fowler, Faulk, Broberg, Suter, Leddy.