Why are those two models competing? Couldn't it be that SMBH are formed via both direct collapse and accretion? Finding evidence for one should not rule out the other I would think.
Generally in astronomy, physical processes have so many orders of magnitude to work with that if you have several physically possible mechanisms, one will be many orders of magnitude more effective than the others and will completely dominate. It's fairly unusual for there to be some sort of "cosmic coincidence" that leads to two processes having almost exactly the same effectiveness. (Type Ia SN may be an exception to this --- they may be produced roughly equally by accretion from ordinary stars and WD-WD mergers.)
