What you are describing is a natural progression for many people. Byron Ferguson, in his book, describes a classic gap system, but then concludes by more or less saying that after a while your mind/body connection will learn how to set the gaps without your having to calculate them, which is instinctive gap, or split vision. We don't know if Howard Hill started off with classic gap, but we do know that he ended up with split vision. In discussions with Rick Welch, I think he went the other way: he started with pure instinctive, but soon discovered he could shoot more consistently if he paid attention to his sight picture (but without estimating distances), which seems to me to be indistinguishable from split vision.
The advantage of split vision over gap is that no cognitive thinking is involved, which opens up the mind to a greater state of physical awareness, meaning that we can be aware of and quickly react to small physical changes that might escape us if we were calculating things in our heads.
The advantage of gap over split vision is that at known distances, we can achieve a far greater level of precision because we have practiced and practiced at those distances until we know exactly what the gap should be.
Given the uncertainties involved in estimating distances, I see no advantage in gap over split vision when shooting at unknown distances.