When I used to consider myself a "gentle parent" there were still always three hard boundaries - respect for people, respect for property, and respect for resources.
So nonsense like breaking a teapot to find out the consequences wouldn't be a thing, because the teapot is someone's property, could be dangerous when broken, and even if it was unwanted, it could still be used by someone else so it is a waste to break it.
I do agree sadly sometimes it can be an extremely well meaning thing which backfires. My mum was probably a bit gentle parenty because she had a very overbearing childhood and she didn't want that for us. Luckily DSis and I are fairly naturally empathetic and don't tend to push things too far anyway BUT I feel as a result of never ever being pushed out of our comfort zones we have both struggled - I find it really difficult to enforce boundaries with others (and have struggled with DS which is probably why gentle parenting appealed to me as it let me off the hook!) and DSis struggles to get out and do things, make friends, get a job, move out of home etc. She really finds decisions hard and lacks self confidence. I've been lucky to have always been social enough that I've ended up having experiences which have pushed me, but been the social pushover instead!
I agree that boundaries are really important in order to model assertiveness to our children as they learn how to enforce their own boundaries from being on the receiving end.
I don't consider myself a "gentle parent" any more because at some point it all becomes nonsense and you drop the labels because you're just parenting - like everyone else and muddling through.
I do believe it's possible to manage 100% of parenting issues without negativity or punishment - in theory - in reality, it's an extremely rare parent who actually has the energy. And it really doesn't matter if you use a shortcut once in a while. Your children won't be damaged by it and they will still learn what you intend especially if you back up the message in other ways.