I think they are probably harmed more than C4 were too by the presence of Big Brother. At least C4 could always argue that Big Brother had helped fund shows like Dispatches, Channel 4 News and other content that ticked the PSB box, but C5 is very much defined by it now and is hurt both by not seeming to target the audience outside of the series run, but also not appealing to the non-BB viewer much either.
If you use 5 News as an example, who is it targeting? There's certainly been a slant towards an older audience when Sky took over the contract, but ITN haven't been able to revert to the original template and are in a quandary. It feels like a tick box obligation in the same way London Live do it half hearted too.
Dirty Des at least tried to add Big Brother demographic style programming around the show, yet BB is now a N&S legacy format which Viacom will find hard to shift.