I would agree that what you describe here did have its occurrence to a small relative degree from time to time and place to place. But it was hardly common place that vassals were able to choose their lords freely as you suggest, before or after Gregory VII.
The very fact that the controversy took place is sufficient to prove my point, that neither the church ran the state, nor the state ran the church throughout the Middle Ages.
Actually it does provide a good example that proves that the church from time to time ran much more of the state in particular territories than just religious matters. Other examples during that same exact century can be brought forth showing the secular government controlling the church. The back and forth nature of the chaotic church/government relations of that time only demonstrates that their were super states, that the church from time to time was the super state, that the church at other times was nothing more than a vassal to a non church super state, and still at other times shared power with super states. Your whole idea of a "proto" system of stability did not exist during the times you speak of.
Do not forget though that we are talking about a period of roughly 1000 years.
I'm not forgetting. In a prior reply of mine I asked for some specificity so as to look at this period in the best possible light to your case. Even here, it is impossible to discuss this matter without specifying the years when this 1000 years began and ended. If you would select the best century out of those unknown 10 centuries, then maybe we could better discuss this proto system that I say never existed.
I talk about the principle. You talk about outcomes. In principle, the society was organized around voluntary exchange of goods and labor for military protection, which is vassalage. The outcomes rarely demonstrated fluidity of vassal-lord relationship because in general trade and movement was restricted, and because the nature of loyalty is such that it is a coin of value only if changed extremely rarely.
The back and forth nature of the chaotic church/government relations of that time only demonstrates that their were super states, that the church from time to time was the super state, that the church at other times was nothing more than a vassal to a non church super state
It demonstrates that the state and the church were orthogonal structures of power that coexisted in tension.
select the best century
West Europe, 400 - 1400, take your pick. The early Middle Ages (till 11 century) had a better pronounced anarchistic system of self-government and voluntary vassalage. In the High Middle Ages (11 - 15 centuries) monarchies began to appear, offset in power by a more centralized and politically assertive church. Quality of life and fecundity of culture were markedly better past 10 century.