Hi Zero_Daye!, I've seen a couple of threads informing the respawning rates of quartzite, so I'm sure the developers are aware of this by now.
The Axe 2 actually cuts down weed "trees", that the Axe 1 cannot do, and dependind on the trunk, it can give you up to 12 (in my experiece), weed stems. That's the focus of the Tiers for now, being able to farrm resources that you couldn't before.
Agree with the Blueberry chunks, I tried to do so myself the first time I got them.
About underwater apparatus, I'll only say that there are some outfit parts foun in the code addressing that approach, I'm sure we will be able to do so on the future, kudos to te devs for that.
Hope you are loving the game as we do!