I'm pretty neutral on my thoughts about the reboot. It's not for me and I understand that some people have enjoyed watching it so I don't like to constantly whine and complain about it. But for me it does not match up to the writing in the Prime continuity, especially not to the original series which the reboot shares so many characters and concepts with.
I was looking at parent reviews of OS Ben 10 on the slightly infamous site "Common Sense Media" out of boredom today since I only have one exam left. And what I read has led me to believe that there is a huge reason why the reboot seems to be restraining itself when it comes to everything to storytelling to character development to the transformation sequences and even the art style: because CN don't want the parents to be concerned and then ban their kids from watching the show (which would lead to less toy sales and profit). I will say that there are a great deal of parents who do approve of and highly recommend the show and deem it perfectly watchable for kids, although sometimes it may be worth having the parents watch it with them. However, there are also some parents who do not like the OS at all. Many seemed to be concerned that because the show had so many action scenes and admittedly brutal fight scenes, it would lead to their kids becoming violent because the kids couldn't differentiate between reality and fiction. They also seemed to despise how the relationship between Ben and Gwen was presented and how Ben was not a good role model for children due to his cockiness and immaturity. The alien designs also seemed to strike a nerve because they looked like (I quote) "something straight out of hell" and apparently some were far too scary.
To all of that, my main response would be that Ben 10 was never meant to be a show just for kids, which seems to be a mistaken impression shared by many parents. It was made first and foremost to be an engaging and compelling show for all ages, with the main target demographic being 10-14 year olds - so not little kids. Yes there is violence but it is not graphic and in my view is necessary to an extent given that it is an action show. The relationship between Gwen and Ben is presented in a very realistic way rather than a 'candy' way (as I read someone saying on the website in defence of the show). They argue and bicker like siblings and are indeed imperfect characters but they do grow throughout the show and actually end up being more relateable for those watching who also aren't perfect. As for the alien designs, well, they're meant to be aliens and not superheroes in suits. Of course they're going to be weird looking and occasionally intimidating. I always thought that the designs were great even when I was much younger.
So my conclusion from this? The opinions of a significant portion of parents (as I imagine that these views would be echoed outside of review websites) explain A LOT of the changes which we saw the reboot. The alien designs were changed to look more humanoid and less alien looking and "scary", and the art style was made simpler with a brighter colour pallet to stop younger kids getting scared. Ben and Gwen's relationship showed them getting along for the vast majority of the time to apparently set a better example to kids. The fight scenes are far more toned down and less creative than the original series. The villains are not as intimidating and there aren't significant consequences. One of the major reasons for so many of the reboot's changes is because the network wanted to cash in on the viewership of the younger end of their demographic of 5-10 years old, and so toned down the show so that their parents did not prevent them from watching. This might explain why a lot of Cartoon Network's shows are toning it down these days especially when compared to the mid 200s era.
I'm really not trying to diss the parents here and I totally empathise with their concern for their children's wellbeing. Parenting can be rough at times (or so I am told by my parents). For me the solution would be to have sensible discussion with the kids and allow them to understand that lets say, Ben only fights against criminals or other really bad people and never used his aliens to attack anyone else . The misconception of 'all cartoons being for kids' often leads parents to make the mistake of allowing their young children to watch animated programmes which may be too complex or dark for their age, and then with the parents subsequently blaming the programme, it leads to CN making things more younger kid friendly at the cost of alienating the older side of their fanbase.
For me, my parents were always cool with me watching Ben 10 as long as I didn't watch too much TV and as far as I remember I never developed behaviour problems while watching the show. In fact I'd think it's the opposite - I thought of Ben as a great role model while growing up, and the fact that he was imperfect only made me relate to him more.