I believe that the issue of aerobatics ok but not cleared for spins is due to a number of issues such as:
- non standard spin recovery techniques
- a/c stability and ability to recover at various stages of spin, incipient or fully developed
- engine stopping during spin necessitating air starts (eg Robin 2160s - good fun when this happens)
- spin stability characteristics depending on CofG position and different weight loadings
It is not really a function of 'g'. There is very little loading on an airframe when spinning (typically 1g). Flying normal aerobatics within acceptable airframe tolerances and not inducing 'rolling g' etc is part of the 'utility' category for which that aircraft is certified. Certainly bodging a manouvre potentially causing a spin (eg screwing up a hammerhead or an immelman) from which a spin could be unrecoverable under normal conditions would prevent me from trying it - or maybe they just never tested all aspects of spinning properly - I think this is the case with the RV7 if you dig into their website.
K