That’s strange. The other two dongles are designed for headphones yeah, but I wouldn’t think that would make a significant difference at all.
Wondering if that cable is primarily intended for a line input rather than a line output? Can the choice of DAC in the cable affect the output level?
My preferred choice of device for your situation is the Rode AI-Micro. It’s tiny, lightweight and has the advantage over your other options of having audio in and out at the same time. It basically lives as an extension to my headphone cable, and I just swap the lightning/usbc/usba adaptors it comes with depending on what I’m plugging into.
Or alternatively I use its headphone out as a line out from iPad all the time into say digitone if I’m playing along to a tutorial or something.
It’s seriously one of the best friction reducing purchases I’ve made, because it’s so easy to tack it in to whatever you’re doing if you decide after you get setup that you want to record or whatever (you know those ugh cbfd moments).
Thread about it here: Rode AI-Micro and/or other tiny audio interfaces