Athos is a great set stacked with both DEX & Crit power. RDM's best, and to my knowledge, only gear for crits are really Nef & Rancor. This along with the poor DEX gear RDM generally gets is the main problem with CDC/Almace.
If you look, currently our arguably best head is Maat's Cap, body is either Ant, or Kudzu, hands are Alucinor Mitts, legs are Tumbler Trunks, and feet are Lithe Boots. Athos would smash most of this gear by far, and is much more useful. Athos Boots trump Lithe in every way, Athos Gloves are a Maat's Cap on your hands, and beat out Alucinor, Athos legs may lack the Attack of Tumbler but make up for it in the crit damage+, and the body has tons of DEX along with the crit damage, not to mention the set bonus effect of crit rate+ which we would get from it, it over all is a massive player.
In the end admittedly RDM lacks DEX gear & Crit gear, which is why Excalibur is much more on par with it than it would be with Athos. Much of the same can be said of Oce/Toci's but I have said that many times all over the place & don't want to re-explain how good Oce/Toci's would be both for TP & WSing on RDM. In the end they are very big players with CDC & Almace, that is the reason of why.
To put it in easier terms I suppose, and a much more simple way, RDM lacks the DEX/Crit gear to make CDC truely as useful as it could, just look at these 2 sets.