I do feel like some of the flourishes require a buff, as a few of them feel like a no brainer picking them. There's only a few times i try something else when using a certain build.
I feel like it's weird adding mettle into the game when there's already a progressive system and helps you in runs, perks. A lot of the upgrades with mettle and are just number changes and don't really add anything interesting, compared to perks which can add different playstyles and more interesting affects. Needing to buy upgrades during a run instead of out like perks do feels pretty weird imo.