The camera used to test a lens affects image quality. The exact same lens can be moved from one body to another with very different results.
The Digital Picture prefers to use Canon bodies, but Tamron makes lenses for multiple camera mounts. Reviews from multiple sources, using different bodies and copies of the lens, are likely to havereport different results. (While you specify you're interested in the EF version, it's unlikely that every review you've read is specific to the EF version.)
Different Canon bodies also deliver different results with the same lens. If you compare the Tamron 100-400mm f/4.5-6.3 Di VC USD on the Tamron 1007D mark II -400mm f/4.5vs-6.3 Di VC USD 1Ds mark III on the 7D mark II vs 1Ds mark III, center and mid-frame look better on one, while the edge looks better on the other.