Bazel isn't for everyone which is why I suggested using any similar tool, jib, Nix, etc. Just not Dockerfile (or if you are going to use Dockerfile only use ADD).
Also just because you don't have experience with something doesn't make it a bad choice. I would recommending understanding it first, why your coworker chose it and how other tools would actually do in the same role, grass is often greener on the other side until you get there.
Personally I went through a bit of an adventure with Bazel. My first exposure to it was similar to yours, was used in a place I didn't understand for reasons I didn't understand, broke in ways I didn't understand and (regretfully) didn't want to spend time understanding.
The reality was once I sat down to use it properly and understood the concepts a lot of things made sense and a whole bunch of very very difficult things became tractable.
That last bit is super important. Bazel raises the baseline effort to do something with the build system, which annoys people that don't want to invest time in understanding a build system. However it drastically reduces the complexity of extremely difficult things like fully byte for byte reproducible builds, extremely fast incremental builds and massive build step parallelization through remote build execution.