Thanks for providing your detailed feedback! I've received a ton of great feedback from the demo which I have been taking into consideration in updates and changes to the demo content.
In the future, the layout of the opening caves area will be reworked/streamlined. The general trajectory will remain the same, as the point of getting the blast pods before the sword was to discourage up-front fighting early on and focus more on puzzles, but I hope the update will smooth over the bumps in the flow of the beginning. Gemfruits do have a use near the end of the demo in the optional path on the west 2F side of Antfort, but there will be additional uses for them in the revision.
The difficulty of the bosses is something that has been on my mind a lot in creating the game. While I would like to avoid comparisons to Dark Souls whenever possible, the point of having the bosses be initially very challenging is to push the player to not think about them as duels/sword bouts and instead as puzzles to solve. On the one hand, they can all be brute-forced in a more difficult way, or, once a puzzle solution is discovered, defeated very quickly and easily using the mechanic, providing the option for players looking for more of a challenge. That said, I did recently revise Antonio's behavior to reduce the number of attacks between charges and stickerball drops because as you mentioned, it was taking too long to get a shot at him.
Thanks again for playing, and hope you enjoy the remaining demos!