Hi Mihai,
I hear you and understand what you are saying. For exactly this reason I suggested in the Jakarta EE spec committee last year that compatible implements list the components that they are using here:
https://jakarta.ee/compatibility
As far as full implementations are concerned, and how innovative (different) they are, it's a more difficult topic. In the current crop of compatible Jakarta EE implementations we see for instance that GlassFish and Payara use the same core- and external components. Nevertheless, Payara is not just a rebranding of GlassFish, far from it. It has many individual extra features (MicroProfile, extra authentication mechanisms, totally different hazelcast based clustering, remote EJB over HTTP, etc etc). JEUS has many similar components as well, but is not a GlassFish derivative; it's a unique server product that just uses most of the GlassFish components for the separate APIs.
WildFly and JBoss EAP are basically the same though, where EAP is essentially a specific snapshot from the WildFly branch and then stabilised/hardened (extra bug fixes, tests, secure build, etc) and supported. So as products they are two different things and it makes sense IMHO to certify those separately.
With Piranha we're also trying to build a Jakarta EE product, and it takes a middle approach kinda like JEUS but also like the now defunct Jon AS; all the server bits and the Servlet, JNDI and some other implementations are our own code, but for Jakarta Faces, Jakarta REST etc we integrate existing implementations.
Kind regards,
Arjan Tijms