If LL would just implement the basic polygon-editing-tools into the viewer, you would still have to learn them.
With 'basic tools' i'm still pointing at Wings3D. This would be the amount of useful tools for mesh- and it's UV-editing. If you call this 'a mass to learn', then you maybe just overrate it ? It must be learned - in- or off-world.
Since i like many, pay a lot for SL, alts, land,...: I more than expect that LL provides, maintains and develops the basics/grid - i insist on it.
Regarding the feeling of building live in-world: I know it and like it.
However, 3 years ago, when sculpties came into a vague beta - my world didn't go down because i had to sculpt in an external app. And when i arranged and scripted the sculpts inworld, the nice feeling was back again .
Animators would have far more reasons to call for in-world tools, seriously. While a mesh (assumption) will inworld look exactly like in the external app, animations heavily suffer during their import. Animation upload causes a lot of trial, error and gray hairs.