It's not an absolute, but a contextual thing. For a clean build, on a single machine, under normal circumstances, gradle will often outperform bazel, because bazel pays a cost for isolation, parallelism infrastructure, and trying to max out your machine. OTOH, the abi-based compilation-avoidance, higher sensitivity to caching opportunities, and parallelism can make incremental builds much much faster on Bazel. Add in test-result-caching for non-flaky tests, and it's really a solid win for builds that don't invalidate most of the build graph.
So it depends on (a) the shape of your graph, and (b) the nature of the change being built (e.g., does it invalidate a core library and all its downstream, or is it close to the app?).
The other thing is remote build execution - the high focus on hermetic builds and parallelism makes building on a cluster of build workers extremely powerful, reducing build times, reducing load on developer machines, etc. And there are out-of-the-box solutions, initially from google on GCP to let you do this yourself.
So... is bazel faster? Hell yeah, in some situations. Kinda in others. Not in some others. You need to think through what your development model is, your scale, how you construct (or want to construct) your build graphs, isolation of components, etc.
