I'll throw in my own two cents here and then some opinions that have been on my mind~
I'll start by saying I think I'm a little biased, I'm not interested in synths because of how realistic they can be. That being said, I consider "over tuning" the overuse of vocal techniques used for expression, primarily vibrato, growl, vocal fry, and vocal runs. In singing, it's absolutely possible to over sing a song, so I think over tuning can be a fair criticism sometimes. In synths, the one I see most often is overuse of vibrato, and it just ends up making vocals sound really shaky, even if they're intended to be powerful. When I was more involved in singing/performing, the advice that was always given to me was you don't need anything fancy to be a good, emotional singer, and in fact, sometimes all those extra decorations can distract from the emotions you're trying to convey. They should be deliberate decisions, used sparingly for that real impact, and not something you use just because you know how. I think that holds true for vocal synth covers in a way too, but I almost never go out of my way to listen to covers to begin with.
Though I also appreciate over tuning if only for the fact that it keeps the art of self-tuning alive in the midst of AI synths where everything is automated and quite honestly, singers sound much less unique in songs. They sound good and make the process easier, but part of a Vocaloid song for me is recognizing a producer's distinct style, I could always tell which producer it was from how the vocal sounded, even if they tried something completely new in composition.
I guess to continue from there, I feel really conflicted about Gumi on SynthV. Nothing against the VB at all, and I'm really, really happy about this new normal of voices on multiple engines. I think it's just the nail in the coffin that realistic voices and AI isn't really what I am looking for in synths. Don't get me wrong, I own a lot of SynthV VBs and I really enjoy using the engine, same for CeVIO AI and Voicespeak, but as a listener, Gumi V6 and SynthV probably won't be what I think of when I think Gumi for a long time, and they probably won't be my preference in finding Gumi content. I really am that person that is an avid user of AI synths, but will never go out of my way to find content with them because when I'm in the mood to listen to synth music, I want that synth sound.
And a couple Miku-centric ones I've been thinking about: I don't mind the lack of development news on Crypton's end, and I personally don't think Miku really needs any new VB at this point other than for modern PC support. For a lot of other voices, updates are a way of keeping a voice fresh and relevant, but Miku has been so much more than just a synthesized voice for so long. To me, whether or not she gets new VBs won't change my decision to use her or listen to her, she's absolutely still the voice I listen to most and V4X is still a really strong product imo. If NT got more public updates/releases or if Miku got a new VB elsewhere, I'd very, very likely still be interested in buying it, but I'm also just happy with Miku.
And the big one to end it off, I massively prefer Miku Expo as a VR experience than in-person. An in-person concert is a really cool experience, and I think every Miku fan should get the opportunity to see her perform in that setting, but after the first couple times, I think the biggest draw of a concert like that is the community aspect and getting to find other Miku fans. There is only so many ways you can innovate and build off a concert with a fictional star. Seeing Miku in my world is great, but I personally love the creative possibilities of going into Miku's world. I guess I just always loved Project Diva PVs, and a VR Miku concert can really feel like you're being pullled into a PV and watching it all happen around you in a really cool way.