Using a pH tester, mine are usually between 5 and 6, depending on additives. I have very dry, curly hair, and don't honestly notice any difference between using bars anywhere in that range.
I get what they are saying about not using oils in shampoo. At the same time, I suspect that some of the oils and other hardening substances are used to hold the SCI together in a bar form, if that makes sense, and perhaps to slow down the rate at which the surfactants combine with water and get used up. I'm no chemist, so feel free to correct me if I'm wrong on that point. I also know that castor oil is supposed to have qualities beneficial to the scalp, so it may be that it's used to somehow balance out some of the cleansing qualities (similar to using different FAs or SFs in soap, although by different mechanisms, of course).
I'd be happy to experiment with some no-oil bars if someone has a suggested recipe. I think that's similar to what
@Tammyfarms was trying in her BTMS-free bars.