I agree with your overall point but Rip seems agnostic on bicep curls. He's been asked on his podcast whether some can include them and his general reaction is "Sure, you can do bicep curls". He doesn't seem to think they're necessary but also doesn't shut down the suggestion as frivolous either.

>which is in the official program and he insists on overhand because it works more muscle mass

I assume this was a typo. But he does advocate (supine grip) chins because they involve more muscle mass (the biceps, specifically). He writes about it in his SS introductory text and also includes chins in his programming section of that book. That book also has a section titled "Ancillary Exercises".