As far as the knowledge of the previous BP goes... really more than anything I think the point of that was for him to be able to communitcate with his ancestors, which of course inevitably sets up the divide he has with them when he can't set off the bomb in Time Runs Out. That was less a power and more a set up. Really they never gave any useful info to him... which in hindsight didn't surprise me that much because frankly I thought T'Challa was smarter than any of the previous BP's anyways. I think he does go to them for a bit of info in Coates run, even threatening them with his spear if he doesn't get their cooperation... but for the most part he already knew more than them anyways.
Shuri isn't one of the 10 smartest people in the world (like she is in the MCU) so her being a Wakandan wiki page gives her a bit something extra. I see your point about Shuris power trumping T'Challa's… but I think Shuri frankly needs it more. T'Challa can still be the go-to person on pretty much anything OTHER than Wakandan history. And he can do it without powers.