Think I understand some of your concerns, but if the glide slope gradient on an ILS is perfectly achievable for a B777, why is there a need to adopt a more shallow approach on a VSA?
When left unchecked, I've seen A320/330s and the like at 2500' with 15miles to run.
Precisely why I never call "visual" until I'm either in the zone or at the last assignable level before the zone.
If you weren't to call visual until within my CTR then you'd likely already have been taken out for re-sequencing via an instrument app.
Also, what 'last assignable level' are you referring to? 500' above the CTA step adjacent to the zone, or other lowest safe?