I got to the last boss and couldn't beat it. (Mechanics spoilers) I used water then advanced time until the shield rusted. This meant I was able to do damage but only about 30 damage with my strongest hit (Water). The damage never went up, and the boss was attacking me with Hyper Volcano Fire hitting for 12 damage about five times in a row. I only have two healing potions and one revive available. It seemed like no matter what I did I couldn't do enough damage to win the fight before I died.

I watched a video on You Tube and as soon as the guy in that video caused the armour to rust his Water attack was doign 145 damage. Did I do something wrong or is it bugged?

Those fire attacks can actually be deflected/parried to decrease damage. After I figured that out, the battle become somewhat easier. Also, you can confirm the water attack at the moment of hitting for some extra damage (got 34.. instead of 27). But initially it seemed to be impossible for me too... Yeah, I saw similar video. It was 10 months old... Could it be, that game mechanics have been updated to relay more on blocking? But then, that does not explain damage difference. Also, after making shield wet and switching to future they never mentioned something happening to shield - unlike in the video.

There is another video were the producer? of the game talk about the feedback they received from the first demo, one of the things was about that the combat was too simple for some.

Maybe they changed it because of that.

Also in my game the characters made a comment about the rust in the shield, I can't remember if it was the same that the video you are telling but there was one.

Ah this is problematic. There is a vocal crowd that wants to make games annoying to play, this crowd will save scum and study videos in advance to "play" and will just not play the game if they still can't win, and then complain it's too hard.

Some devs put in difficulty levels and permadeath options to cater to these types. These types will then simply ragequit and make backup save files to avoid the permadeath (why even use that option then I don't know). But at least they don't ruin the base game balance.

When a dev changes the base game to cater to them, it definitely means they aren't interested in the silent majority, especially for a genre like JRPGs, which were never about difficulty. JRPGs traditionally appealed to people that liked reading a lot (this has changed with VA as well honestly) and wanted a more casual play experience. There is room to play multiple things, I used to primarily play fighting games and JRPGs, and that was an extremely common tandem of genres. Fighting games are considered one of if not the most difficult genres out there, while JRPGs would generally be one of the easiest, different experiences for people to select for.

I was able to just deflect the attacks easily but that's really not what I'd be playing for. When I want to parry I play Third Strike, I don't need that in my JRPGs.