The B-2 and F-15 were both in the days of the multi-role thinking. They both prove that multi-role aircraft are inferior in specific tasks. If these planes were not capable, or even superior, then why would they keep them around.
No one aircraft alone can be the master of all trades. The B-2 is a better bomber than the F/A-18. The A-10 is a better ground attack aircraft than the F-22. The B-52 can only be matched in carpet bombing by the B-2, another bomber. The F-15E surpasses all but the F/A-22 in the fighter role.
Multi-Role aircraft are a jack of all trades, a master of none.