The min bounces parameter was simply something that was added back to Cycles as part of resolving a quality regression, adaptive sampling would be an entirely new feature that won’t be in 2.8 because of the feature freeze.
Still, while having the min bounces at say, 10, doubles the rendering time, the convergence rate goes up many-fold with scenes highly dependent on indirect lighting and especially with scenes containing volume shaders. That in itself can be considered a great improvement over automatic RR.
In addition, there would be a reason why automatic RR is default and the parameter is in the advanced subpanel, there’s a point where you get diminishing returns in quality improvement while the rendertime increase remains linear. It is not recommended to disable RR completely by having the min bounces and max bounces the same. Some scenes also benefit way more from it than others as already stated.
EDIT: Here’s the devtalk thread that convinced Brecht
A number of professional users said the automatic RR made Cycles unusable for them (which could’ve meant noticeable consequences for the dev. fund and Blender’s place in the industry). It was argued that reintroducing the feature would’ve meant rolling back various speed improvements, but the penalty was high enough to where they couldn’t make up the difference.
