Horizontal progression? In MY theme park?!

[Remedi]

At this point you could just create a rune system for skills like D3 instead of relying on materias.

That said while I would agree that materias could be better, this doesn't really adds to gear variety.
Unless we start making materias slots color based and more complex.
More like FF7 perhaps at that point some pieces of gear could have some more interesting effects.

Maybe like linked materias slots where by taking your examples you could link avenger's shield, heavy shield and shield lob together

However as some have said we lack the variety on job skills to make it really work