In the “where to aim long-term” section, you do not mention Commissioners’ cabinet of advisors. I’d be curious to know why, as I thought these roles are quite impactful (though very political). My understanding is that Commissioners’ cabinet members steer policy issues, not only in terms of substance of legislative proposal but also during negotiations with the Parliament and the Council.
My guess would be that DGs & Secretariat General’s freedom to influence a policy area is inversely proportional to the extent the relevant Commissioner’s cabinet cares about that policy area: if the Commissioner’s adviser in charge makes it her or his pet topic with clear ambitions, the DGs staff will be constrained. For example, GDPR is reportedly the brainchild of mostly one advisor to the President of the Commission. AI has become so politicized in the EU that VP Vestager & Commissioner Breton have already been quite vocal about it and their cabinet members are therefore following DGs’ work on that matter very closely (of all the files in their pipeline, it is possibly the closest to a career-defining policy issue).