Under Brown as captain we've failed to get past Braga, Utrecht, Sion (then got entry), Legia (then got second chance), Maribor, Malmo, AEK Athens, Cluj & Ferencvaros. That's Qualifiers during the Summer to get into the CL or EL all against teams we should be beating. That's not even including failed ties against teams like Inter, Zenit, Copenhagen etc after Christmas.
That's a shocking number of failures under Brown as captain in Europe, we also didn't win a Treble under him as captain before Brendan arrived who proved to be by far the biggest difference to the domestic dominance that followed.
I've just never bought into how much he truly galvanizes the team due to the high number of Europe & domestic cup failures (pre Brendan) he's been captain for.
But anyway that's just my opinion, it's the manager that makes the biggest difference always.