ViVid is a strange manga. It feels less like a standalone story and more like the prequel of one due to certain unorthodox decisions it makes. I would have to guess those come from it being the first long story original manga from Tsuzuki Masaki: While I didn't like the reading flow of the manga very much, it wouldn't be strange in a Visual Novel, while I had problems with the "lack of commitment" problem in the manga, such problem wouldn't be there in a short anime. Nanoha's storylines usually follow the structure of one of our heroes wanting to offer help to one of our antagonistsin order to try to achieve a non-violent solution: This is the case with Nanoha and Fate in the original, Nanoha+Fate and the Wolkenritter in A's, as well as Erio+Caro and Lutecia+Garyuu & Signum+Reinforce Zwei and Zest+Agito in StrikerS. ViVid decides to flip the concept on it's had by asking "But what if our antagonist accepted our hero's help from the very start?", trying for a more light-hearted and low-stakes approach, but having problems in it's execution.
While it's first three volumes seemed a bit aimless, the start of it's tournament arc made it really seem like the series was finally taking shape in a way that reminded me of "Gunnm: Last Order", and that was somewhat true as there is a story that is somewhat completed at the end of volume 12 with a thematic ending... the problem being the strange spot the series as a whole is left after that, as there's no longer enough "time" to make some big arc, it's remaining volumes now being a sequence of small gimmicks, similar to it's first 3 volumes.

Here's why the definition of it looking more like a prequel: It introduces dozens of characters, but does nothing with them. While one could argue that StrikerS did the same, the reality was that StrikerS did so by being in the structure of a "large last arc", by having every character do "one last remarkable action", which is different from having a character do a single thing in the beginning or middle of the story and them be relegated to only being in cameos. This creates a vicious cycle where instead of reusing characters, we keep making new characters to be disposed after being used once (e.g. Chantez, Tao, Fabia) or never used at all (Yumina being the biggest example).
While this could be said to being a problem of the Nanoha franchise AS A WHOLE, it is something justified as it was done between three different series separated by time-skips. If you do it in a single series that's supposed to be coherent and happen in the span of a year, it becomes egregious.

Vivio is barely a protagonist for most of the series, that function being mostly divided between Einhart and Miura. There's also a constant problem (Could be because of editors telling the author to "wrap things up" or the author himself growing tired of a certain idea) of the manga doing "tell, don't show": If there are three fights, we will only be shown one of them and be asked to "imagine" the following two, being told what happened in it. If there is a five day trip, we see two days of it and are told what happened in the remaining three. The most egregious example being a certain tournament where there is a full chapter for the first fight, but them a time-skip and a single page for the semi-finals and finals.
Once again: ViVid does not commit.

While it fails on the macro scale, however, it does succeed in the micro scale: To present a character, make us care for them and having them have a motivation for one or a couple fights where it really is well executed (Once again, something that worked masterfully in StrikerS), the best example being the character of Corona, currently the top 3 ViVid original character with the most favorites, losing only to Sieglinde and Einhart.

There's also a curious case of "suffering from success": The new characters are presented as so powerful and having abilities so interesting that it makes it seem that characters from previous season (That should be stronger than them) are weak by comparison. StrikerS didn't have such problem by having a more "grounded" setting, where the powers of every single characters seemed simple, yet interesting, it was believable that Nanoha was a behemoth compared characters such as Subaru or Teana, but compared to the flashy powers of characters in ViVid such as Rio, Victoria, Sieglinde or even Einhart, the series fails to make her seem more powerful than a generic aerial mage even though, of those, only Sieglinde would stand a chance against her in a fight.

Talking anymore would've been just me repeating myself, so let's conclude: Don't be deceived by the high chapter count, this isn't a series that will use them to have many long, meaningful arcs or to work or develop most of the characters it introduced. If something, it's almost a gacha in the form of a manga, and this isn't changed by some very good moments it has here and there.