Batman: The Animated Series had none of that stuff and is largely considered to be more mature in the truest sense of the word than most actual "Adult Animation".
I just think that sometimes fandom can be a bit.... bludgeon-y (as opposed to
Bludgeon-y 
).
Like... cards on the table? I love BTAS. Batman is one of my favourite characters in pop culture, and BTAS was in many ways my intro to that world, to the point where I hear Kevin Conroy's voice in my head any time I read Bruce's dialogue in a Batman comic.
But... and this may not be super popular in these parts... I kinda find it irritating when people either put it WAY up on like five pedestals or use it to put other versions of the franchise down. I'm just kind of over some people always bringing up BTAS when trashing whatever live action Batman series offended them that week.
It's a good show. Amazing even, and you're not wrong about the maturity level... but it's also not perfect. It can be dumb or goofy at times. None of this takes away from it, but I'm tired of everything being held to some impossible gold standard that even the thing in question didn't truly live up to.
Circling back, you mentioned a great CS Lewis quote, about how nothing is quite as childish as the desire to seem very grown up.
Which is a great quote, and one we in this fandom (and others) should take to heart.
But I also feel like it's used to bludgeon... well... topics like this.
Like BTAS, I've heard so much about how Rescue Bots is the greatest Transformers cartoon of the last fifteen or so years, and how it just embraces being a fun kids show and isn't afraid to be what it is, and it does it so well...
...only unlike BTAS, I've never seen Rescue Bots. And truth be told? The energy and forcefulness some of its fans push it any time it comes up make me not want to engage with it. Chances are it can't possibly live up to the hype that's been sold to me, even if it is quite good in its own right. The eagerness to use it as a shining becon has made me not interested, just how like the eagerness to always praise BTAS, even if it means bashing other adpatations, has made me weary of a show I genuinely enjoy and have many fond memories of.
And to take this a step further, yes... edginess and excessive violence, gore, swears, and sex are very adolescent, ie not really mature... but this "it's childish to want to seem grown up" mentality now seems like a fandom sacred cow in some circles,
where if you even ponder the idea of a Transformers story that dares to actually try to be a bit more mature with its themes, you get lumped in with the Buckets of Blood crowd. And it can be frustrating, in terms of discourse.
This is compounded because
IDW did all of this, and yet I can't help but wonder if the same people pontificating doom and gloom for a SkyBound adapation would be singing a different tune if IDW's stuff was getting adapted instead.
What's wild to me is that this much doom and gloom and "oh no they said 'adult animation' it'll be nothing but blood and gore and curse words" mentality is being bandied about for a show that will be adapting known material.
This will be a show about SkyBound's Transformers comic. A very commerically and critically acclaimed comic. That is a known quantity. You don't even have to read them to get the gist of the story. As of this post, TFWiki has summeries of the first 25 issues.
"OMG IT'LL BE SWEARS NON-STOP" or "OMG THE DECEPTICONS ARE GOING TO VAPORIZE HUMANS LEFT AND RIGHT" like... that's not what this comic is. There is action, there is violence, but that applies to like 90% of Transformers media. This will be a show based on a known comic, helmed by people with a track record making critically acclaimed adult-oriented animation based on comic books...
forgive me if I'm weary over the knee-jerk "they said 'adult,' assume the worst" reactions.