I can't say I agree with your main criticism of the game.
I've put well over 100 hours into this game and none of it felt like a grind. From the footage, you've shown it seems you stuck with the shield most of the time and that might have been your "error". I usually go with the weapon that has the darkness boost and thus rotate through all of them and it makes for deeply varied combat. Especially once you factor in the different aspects for each weapon and the different builds you can construct with each said aspect.
Also, the Pact of Punishment is a great way of adding difficulty to the game since you can customize where the difficulty is coming from and in return you get more materials to upgrade your weapons making them more powerful and more fun to use, making you want to do another run to test them out. It's a very satisfying loop.
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