I'm just bad at parrying in general no matter the game. I want to love Sekiro as it reminds me of Tenchu, which I adore, but even the first mini-boss just hands it to me. I've only ever gotten a few bosses in.
I just spent a lot of time in Korean arcades in the 90s with Street Fighter 2 and Samurai Shodown 2. I think the last two fighting games I really loved was Soul Calibur on the Dreamcast because a buddy and I played it endlessly and VF4/5 because of the godlike training modes.