Well, according to the (4th) Doctor: "Harry Sullivan is an imbecile!".
I decided to do another marathon re-watch of all Who and I've realised Ian and Barbara set the bar very high for competent companions. If you ignore the one or two times that a writer decided Barbara needed to twist her ankle to slow the group or get captured (a common problem for several early companions, and more to do with the pacing/serial nature of the stories) then they both come out pretty well. Ian sword-fights, knows unarmed combat and pressure points, is a science teacher who actually uses the knowledge (rather than needing a girlfriend constantly reminding the audience/Doctor that he's a science teacher), stands up to the Doctor, etc.
And take Barbara, even with some of the almost-unavoidable 60's prejudices that creep into the scripts, she still comes across as strong, independent, and confident in her own abilities. Look at how many times she takes charge, such as in Dalek Invasion of Earth (organising, planing a bombing raid complete with robo-disguises, repairing a 100-year old engine and smashing a truck through Daleks. Not to mention standing up to the Doctor in The Aztecs, route-marching through a swamp on Skaro (in fetching Thal-trousers), solving the whodunnit murder on Marinus, firing a flare-gun at (what she thought was) a monster to protect Vicki.... I can see what Moffat was getting at when he said he thought Donna was how Barbara would be written now.