As a general matter, federal sentencing statutes "permit a court imposing a sentence on one count of conviction to consider sentences imposed on other counts." And nothing in the text of § 924(c) restricts a court's general sentencing authority in this regard.
A broader point of interest in Dean: Chief Justice Roberts appeared to recognize what the sentencing data has shown over the years about offenders "aging out" of recidivism, and the futility of obscenely long sentences:
Dean committed the two robberies at issue here when he was 23 years old. That he will not be released from prison until well after his fiftieth birthday because of the §924(c) convictions surely bears on whether—in connection with his predicate crimes—still more incarceration is necessary to protect the public. Likewise, in considering "the need for the sentence imposed . . . to afford adequate deterrence," §3553(a)(2)(B), the District Court could not reasonably ignore the deterrent effect of Dean’s 30-year mandatory minimum.