Re: It's not You, It's Me
Well, I agree with Cady in that jin does not appear to be as universally nor as explicitly labeled in Japanese arts in the same manner. Where I would perhaps quibble with Cady would be in the details in which jin is being expressed (in this sense) as aiki as I think is steps too far into the application, cause and effect without perhaps enough consideration of all the pieces working together to allow for said cause and effect.
I won't speak to Daito-ryu as I agree there's assumptions of jin expression in the techniques (ie that's why they would "work"). In aikido, the same rule applies, but as has been written before, it is somewhat bundled with a number of other expressions of ki into the umbrella of kokyu rokyu - which again presumes jin as the baseline component to make the other things "work". But because it's even less explicitly called out and taught - unless you steal the transmission from someone that has it via feeling, it's a very perishable skill.
An aside as well - though peng jin is the baseline jin that enables the other jins, there is only one jin. In aiki speak, however you classify expressions of ki (in Chinese terms jin is the expression of qi), you can't have aiki, kokyu, etc, without some degree of jin as the base.