Maybe "Shran's nephew", but Shran himself, I agree, would have been 'diminished'. he was a competent captain in his own right, why be aboard Enterprise? Thats a demotion. Now, if they wanted to do a 2-3 parter with Shran aboard as an advisor (to deal with some species the Andorians have experience with), than sure - thats just a story-arc, and we could have conflict galore (Imagine both Shran and T'Pol trying to take over the Enterprise after something happens to Archer.. that would have been a great moment).
And I never felt T'Pol was diminished in any way (except maybe by the writers) - she was a strong, independent woman who never backed down, always argued with the Captain when she thought he was wrong (and as Data knows, thats the job of a second-in-command), and gave a big middle finger to the Vulcan High Command, even though she knew what she was doing was not only very 'un-Vulcan', but it could possibly leave her an outcast on her own world. You have to have some kind of backbone to risk pissing off your planet because you think you're right. And she 'sparred' with Tucker and everyone else, even getting 'snarky' as time went on. At no point did I ever see anyone 'diminish her' in any way. And honestly, she was one of the very few female characters I think Trek got right. She needed no man to define her. Sure, the writers liked their cheesecake, but that wasn't on her or the actress that played her.
Oh, and Uhura. Thank the space gods they never did anything questionable with her... oh, wait... {shakes fist at newer movies}