Agreed.
Points to ponder are that even within same organization, Long term Release team and the maintenance team haver different needs.
I have hard time buying "All D TRs go to PRD" as Best Practice. Seems to me that you and Christian wouldn't accept it as the de-facto standard either. So, I am not alone. I am afraid to ask my counterparts on what makes this "The Best Practice". Their answer so far is that that is the only way they have seen this world spin. i.e. they are mechanically working transports, and haven't really put any thoughts in it.
Thinking more into this, I think SAP is missing an upper Hierarchical node with Transports. I know it has "Packages" and "Transport Attributes" and some other things. However, each transport must need a release grouping node above transports. The idea isn't much different than the "Package", but the "Package" change prompt doesn't come up for all changes. Packages need to be manually changed. Not everyone can be trusted to manually change Packages after adding and changing objects via TR. This new higher functional node can be used to accumulate at higher level. i.e. no different than "Copy Transport" but Supported and Mandated by SAP for every Transport. I would call it "Code drop group". Along with the grouping, it can be used to identify cross "code drop" dependencies. i.e an object can only be locked in one "code drop group" while the "code drop group" is active. Once this "code drop group" is put in Production, it is considered closed, and can not be re-used.
SAP has SolMan and I suppose it is as good of a CVS as other matured CVSs. However, fact of the life for many of us is that SolMan is not utilized everywhere, and it needs a little different skill-set to support and implement. My beef with "All D TRs got to PRD" is that manual transport building is a Tedious process. I have seen everything that can go wrong with it gone wrong in my 8 years of SAP production support, more than a few times. ex. 1. missed TRs, 2. out of sequence TRs 3. accidental re-imports. 4. Transport list being updated till last minute. Not just in PRD, but also in 2 parallel Dev/QA environments, and copies of production. Only way I can think of to reduce this is to reduce the number of Transports. Not to mention, I can't pitty enough people who feel pride in putting together and maintaining Excels with 100s of Transports.
I guess we have beat up this subject plenty already. However, please do add more, especially if you like my suggestion of having a higher node for Transports.