Given the domestic constraints of deploying conventional forces long-term in the first place, and the difficulty regular forces face trying to partner with and build up host-nation forces, SOF tends to be the logical solution.
The broader issue remains within the responsibility of our government, however, to attempt to identify local actors who are deemed satisfactory partners both from our perspective and that of the nation they will eventually try to govern. This larger decision applies pre and post-conflict, and is not easily reached.
For me this is the primary limiting factor; finding a suitable local partner who supports US strategic interests/influence in a country without violating human rights, and who can simultaneously provide effective/legitimate governance.
Despite the best intentions, funding, and resources, finding local actors who satisfy this criteria is difficult at best. The level of decision-making for this quest is unclear as well: the intelligence community provides assessments of potential partners and theoretically has the freshest information from the ground, and the State Department similarly has a feel for local politics and has a say in who our partners should be. Where FID and mil-mil training is involved, DoD and various subcomponents (specifically SOCOM) hold sway as well.
It is this broader, ugly, multi-layered and multi-faceted question-set that deserves further thought and inquiry before we delve into another foreign expedition, in my opinion.