A VU by definition from Riot was the previous VUs that were given to 
and
. These VUs did minor kit tweaks, and modernized the champions with completely new models, completely reworked rigging and animations, and completely new VOs.
Regarding
and
, their animations are not fine, and what new animations they received were very minor, like a new basic attack animation that played every so often. They did not receive any full scale animation overhauls to remotely modernize them. Hell, neither of them have recall animations, and that alone doesn't put them on part with modern VUs and VGUs. They only received "recall animations" when Riot went through and copy/pasted pre-existing animations to the recall, which is a bandaid, and not an actual replacement for real recall animations. Compare the animations of someone like Sion, who has varied attack animations for attacking not only minions and champions, but also specific ones for attacking turrets, as well as a properly looping dance animation and a fully independent recall animation. And then remember that Sion was reworked prior to both Fiora's and Shen's VUs, and all of it was after the previous VUs of the champs listed above. The standard of quality is simply sub-par, and very half-baked of Riot. MOST ESPECIALLY since they consider what they did to
to be on the same level as what they did to
and
. They're all classified as VGUs on their official updates page, and this is an utter farce because of the sheer lack of quality in Shen, Fiora and Miss Fortune's work. By that extension,
and
are also classified under the same Visual Update category that they lump
and
, and both Mao and Ali received nothing but an exterior model update, with absolutely no updates to their vocals or animations or riggings in the slightest. Sure, Maokai got his VO, but he got it at a much later date, and he's almost had a piecemeal VU on par with Karthus and co, but he lacks the fully modernized rigging and animations to qualify.
So that's my definition of a VU and VGU, the sets of champions that were the consistent baseline for those types of work and what it entailed to fully and completely modernize older champions, a baseline which was complete shit on and thrown out the window when they decided to claim that their work on Shen, Fiora, Maokai, Miss Fortune, and Alistar met these standards well enough to cease completing the work on them.