Gentle parenting I've come to realise just means "Not authoritarian parenting"
That's why it covers the whole gauntlet from permissiveness to bonkersness to normal/sensible parenting, but a lot of gentle parenting resources seem to define themselves by what they are not which is why people come up with definitions of "conventional parenting" which are 50 years out of date and nobody has advocated for for decades.
All modern parenting resources seem to agree that authoritarian is bad, permissive is bad, authoritative is right.
A lot of the techniques explained on gentle parenting sites are authoritative.
A lot of modern parenting advice, even though not labelled "gentle" would fit under a gentle parenting definition of not authoritarian.
Gentle is not a helpful name IME. It just creates entirely unhelpful and completely meaningless camps - because you get people identifying either as a gentle parent or as somebody who is far too sensible to go for this gentle nonsense - and meanwhile they might both be using a very similar approach and probably have things to learn from each other, but the "gentle parent" is put off by the other's hostility and the other is put off by the label.
I've even made a silly diagram to show the overlap IMO 
You have authoritarian (all the shouting, punishing, control, expectation of obedience etc), authoritative (boundaries but kindness), and permissive (no/low boundaries) in a row in red, green and blue respectively. They all slightly overlap.
Then a big "gentle" circle that covers most of both authoritative and permissive. I honestly think there is that big of an overlap. And that's why it's an unhelpful label.