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Cloud Optimized GeoTIFF does not scale indefinitely. It is useful for small to medium-sized rasters, larger national sized rasters would not be well suited to storage in a COG.
COG skips the need for an API by allowing direct access to the raster data. While this makes things simple for COG file access, it is not flexible and means that data stored in vector or another raster format would have to be retrieved by the client in another manner. Making the overall solution less interoperable.