With political consensus reached across Wales and Westminster that the current conferred powers model of Welsh devolution should be replaced with a reserved powers model as exists in Scotland and Northern Ireland, this article looks back at the systems instituted under the Government of Wales Act (2006) and compares it with the proposals contained within the draft Wales Bill (2015) and Wales Bill (2016). This involves an in-depth comparison of the consequences for legislative clarity and robustness of the shift in 2011 from Part III of GoWA 2006, which instituted a system for the ad hoc transfer of powers to the National Assembly, to Part IV, which provides the Assembly with direct primary powers over specific policy areas, and the subsequent comparison of the existing system with the draft bill’s proposals. In doing so, two claims are advanced (i) that the system instituted in Part III of GoWA was actually preferable to that unlocked with the shift to Part IV; and (ii) that this existing system was nevertheless preferable to the proposed reserved powers model contained in the draft Wales Bill. Ultimately, what the Welsh case illustrates is how constitution building should not be done; and furthermore that there are inherent problems regarding legislative competence within conferred powers models of devolution, but that a reserved powers model is no panacea either.