Gentle discipline doesn't mean no discipline. My parents mostly used gentle discipline (they didn't know it had a name, just went with what made sense to them) with my siblings and me and it was very effective, much more effective than the one time I was spanked or the few other times another method was used.
And like anything, you have to make it work for your family and just because someone on here says something is or is not GD, doesn't necessarily mean that is true

I disagree with people on these forums quite often myself

but I still keep coming here because I learn a lot from others' advice and experiences, even when I sometimes disagree.
The book I have enjoyed the most that really helped me get it was
Parent Effectiveness Training. That book explains that it doesn't have to be either the parent wins or the children win, instead everyone can win. Sure, it's not foolproof or perfect, but it really helps change your attitude about parenting, not seeing it as us vs. them or someone has to win and someone has to lose and gives you some good real life examples and good strategies. It's again pretty much the way my parents did things, just they did it because it made sense.