For some time I too have been troubled by the usage of those two and another tag:
coordinate-system (with spatial-reference, crs and srs as synonyms) - 1,850 questions
projection (with projections as a synonym) - 1,672 questions
projection-conversions (with reprojection and reproject as synonyms) - 829 questions
I know that I am not on top of when ...
I can tell you how I would dice up the tags for questions, but as a "power user" in this area, I do not use the terminology in the same way that most general users do and not even as most colleagues understand them.
Note: correct ISO/OGC (International Standards Organization/Open Geospatial Consortium) usage for the georeferencing information of a dataset ...
PolyGeo's answer contain links which explain why not doing this in an automatic fashion.
However, I second your effort on manually filling excerpts and wikis for tags in GIS Meta. I also do that sporadically when I ask or answer a question which have a tag at least with no excerpt.
Usually I will look at the main Meta Stack Exchange site and see if there ...
A feature request like this would need to be implemented at the Meta Stack Exchange level rather than here at Meta GIS SE but it has already been discussed there as:
Unifying descriptions for all tags across SE sites?
which was made a duplicate of Why don't we add a question with the same tag on multiple Stack Exchange sites? and set to status-declined....
I agree with you that the two tags warrant review, and that bringing them to a single tag would be ideal.
I agree with @Midavalo's comment that:
All geotiff files are tiff files, but not all tiff files are geotiff.
I agree with another comment by @Midavalo that:
I can export a map from ArcMap as a TIFF file, without it being a GeoTIFF.
I also see ...
I think in practice, the two tags have been used interchangebly, hence they should be synonyms.
Moreover, the tag excerpts also address a similar method of use, in which the tiff's excerpt reads: use it within the GIS environment, i.e., when tiff files are related to spatial data.
The greater number of questions in geotiff suggest it is the preferred ...
In the same way that it is almost inevitable that different folks will ask similar questions using totally different terms, it is inevitable that tags will be used inconsistently.
Coordinate systems and projections are related but different phenomena. Coordinate systems allow numerical positioning of points in two- or three-dimensional spaces. Projections ...