I wouldn't say the game is redundant, but the normal mode (Darkest Mode) is very grindy, as you need to gather tons of items to upgrade with. The game doesn't keep track of total monster kills or anything, but it does keep track of your total number of deaths (This is important to the hard mode, as you can only let a handful of characters die on the hardest difficulty) The game also keeps a record of the outcome of every quest you undertake and never deletes any of it, so you are able to see how many successful quests you've had in comparison. It is hard, but it's also very forgiving (Even moreso in Radiant Mode).

In response to your other questions, the game is definitely hard. It's called 'Radiant Mode', and it doesn't make enemies easier to kill, but it instead alters a lot of the rules to make other parts of the game faster and easier (for example, it reduces the cost of upgrades for heroes and town buldings to half their normal cost, as well as allowing you to take high level heroes into low level dungeons) The game itself recommends it for a first playthrough. All versions of the game have an Easy Mode.

Darkest dungeon (nintendo switch)