The way I see it, contextual UIs are nice when they surface useful information; otherwise, they're just noise. Showing blame lines in "prime real estate" for contextual info? I'd personally call this noise. Usually, when I want to see which commits touched what, I want this info over a larger block of code.
I also found that commit header line is near-useless information[0] - it's too short to convey anything interesting. In my experience, almost all commits tend to belong to one of two categories:
1. The whole commit message is in the header line. Meaning the whole commit message is worthless anyway, and I'll have to skim the diff to learn anything.
2. There is a proper, multi-line commit message. That still means the header line alone is of limited utility.
Myself, I use Magit's blame functionality, which pops up a buffer annotating the whole file with blame information, grouping lines belonging to the same commit. That said, I still have fond memories for IntelliJ's blame, which put that data in a fixed-width column on the margin, showing author and date. It also colored the sidebar by commit age[1], which provides something much more useful in terms of contextual data: a qualitative indicator of age of pieces of code in the file. This kind of data is what contextual UIs are best for - data you mostly want to keep in corner of your eye, to get a feel about things.
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[0] - I still like it displayed, though: it's easier to use as "visual hash" than date, author or commit hash.
[1] - I'm 90% sure this coloring was in IntelliJ, but I might have seen this in a different IDE.