i think he didnt know how claim system works and stuff
He does know how they work. If you don't mine down to bedrock immediately, it will only claim 30 or so blocks deep. This means people can move in underneath and/or tunnel into your claims sometimes. It isn't until you build that deep that the claim starts extending down. He just wants it to claim all the way down immediately, instead of retroactively when he finally builds that low, which makes a ton of sense.
the claims in survival already go up/down to max height. And if you want to mine there is an resource world free for mining. so -1
And also this suggestion is bit confusing, First you say
"There isn't a need to keep the area under claims available for mining. We have an entire world for mining."
So it looks like you want to be able to mine under a claim, and later on you want the claims should go down to bedrock.(whats already in the current survival mode.)
See above, they don't go all the way down until YOU do.
As for the second part, it's a misunderstand on your part. His assumption is that it doesn't extend all the way down so others can mine under HIS CLAIM. He says that's not important because the resource world exists. This means there's no reason for claims to not immediately go all the way down, because it does. He just wants all of his land saved without having to worry that someone has gone underneath and placed things there