While I like DxO, their lens testing procedure has always been a puzzle.
I remember being struck, for example, by a
Lenstip.com article on colour rendering in lenses and binoculars as an aside praising the DA 40 as a great lense for light transmission ('The [light] transmission, reaching 97-98% in the big part of the visible spectrum with 8 surfaces, means on one air-to-glass surface we lose only 0.2-0.3%.')
And then seeing DxO rate the Tstop of the DA 40 at 3.1, which is heading towards poor.
However in the same lenstip article they profile the light transmission of the Samyang 85 1.4, which doesn't appear to have any advantages over the DA40 in terms of light transmission:
but DxO rate the SamYang much better than the DA40, with a Tstop of 1.7.
And to add insult to injury, DxO's Tstop value for the DA40 (3.1) is is even worse than (for example) the Tstop (3.0) of a complex zoom like the Sigma 24-70mm F2.8 IF EX DG HSM, which is also profiled in the same lenstip.com article.
So something seems amiss. Or maybe I am misunderstanding what they are doing here.