Yes, you are right that looking at one commit doesn't tell you much.
It's looking at the nature of on going changes.
A single complex file written once and never touched is likely a good cohesive file about a single problem solved.
However, if we start making many changes to that file increasing it's complexity, it's likely not the problem getting more complex. It's likely we're adding more purposes to the file, eroding it's cohesion. This is the signal I'm trying to catch to avoid a mess starting.
It's looking at the nature of on going changes.
A single complex file written once and never touched is likely a good cohesive file about a single problem solved.
However, if we start making many changes to that file increasing it's complexity, it's likely not the problem getting more complex. It's likely we're adding more purposes to the file, eroding it's cohesion. This is the signal I'm trying to catch to avoid a mess starting.