Tell you what. Let's go ahead and have you *moderate and run* (not just play with as an end user) a Yahoo group with 27,000 members in your spare time (as I do and have for many years). You get a week to do it with those "ancient" tools and interface, and then another week to do with with the badly broken, slow, ill-conceived, feature-poor, absurdly buggy new interface. After that week - if you can even get through it - come back and tell me that "Neo" is working just fine, thank you very much.
We won't even get started on your false dichotomy - that because some features might have been desired (eg inline attachments, which my users would never want or need) that it was necessary to completely revamp the entire interface and throw out about half the existing functionality to provide them.