I've been chided for not doing this in the past (I just read the code usually) and would actually agree with that person in retrospect.
More generally, studying the code under debugger means you need particular input data -- the one suitable for the part of the code you study. That can take time to get.
Seems weird to say a team was always hung up on ensuring the correctness of their code. I guess it depends on what you work on to an extent.
In fact, isn't this usually the case with any application not yet in production?
As an example, I had a teammate who would get blocked on needing JSON that matched a production set of data. Yet, she knew what the various fields of the data would most likely contain. She ended up writing the code anyway without the "production" data she asked for and it worked great minus a few small changes. It was ultimately just psychological block, IMO.
Since most of the code I read (C# code) can be ran on my platform, I'll sometimes run into that rare piece of code that I can't believe it does what it says it does, in those cases I'll download the repo and debug it and many times be surprised to find there was a gap in my understanding. Reading code helps me find knowledge gaps I didn't even know were there.