In version 2.0 composite components does not resolve default values correctly when a direct call to cc.getAttributes().get(key) is done. Only EL expressions are resolved correctly, because by the spec an EL resolver is added to deal with this.
Testing some stuff on
MYFACES-3168, I notice Mojarra 2.0.6 and 2.1.2 resolves it, so we need something there too. I knew about that problem long time ago, but since the spec mention the EL resolver way to do it, I preferred do not do any changes until 2.1.
In my opinion the best way to solve it is do the same thing the EL resolver does, but on the component attribute map. It is important to take care about performance in that part, because that part is very critical.
The only reference I found about it is: