HN user
I just landed a really great offer in NYC and a lot of it is because of Sarah Chimino at Andiamo (https://twitter.com/schimino). She always had a really positive attitude and I came away with it feeling like she was always going the extra mile for me.
Sorry to vent but...
I had a really bad interview experience with Jet, to the point where I would never shop with them as a customer. They recruited me, I passed two phone interviews, and I thought I did well in the on-site interview. And then... nothing. No feedback, no formal rejection, just nothing. I emailed and called several times but even then I never got a "no" - I would get a "we're still trying to figure out our team organization". There was absolutely no communication from their side at all. So it's several months later now and I've given up any hope of any kind of response. And I'm walking away from the experience just feeling kind of disrespected. (It's a shame too because I would have loved to work at an F# shop.)
Every touch point an organization has with someone on the outside is the opportunity to help or hurt your image a tiny little bit. And I think Jet could definitely use some work in that department.
I think you answered your own question. Of course more abstractions make things harder to read and comprehend. The tradeoff between simplicity and flexibility (and testability) is a design decision that your team has to make. Since this senior dev is a good developer they are probably adding this complexity because they think its necessary for their overall design goals.