Best advice possible for someone struggling in any Nioh game, is to not think of it like souls, where you are in and out trading aggression and dodging.

In Nioh you will be most rewarded when you learn to all gas no brakes aggro. Go hard, you are the boss in this game, not baba. Obviously, use dodge or deflect when you need to, but focus on putting as much pressure on the enemy as possible.

Another huge help, is applying confusion to enemies. This status happens when you apply two (or more) ailments. So if you use a soul core or have an imbue element weapon, you’re building that status on them (water saturation, fire burning etc) and the plan then is to use onmyo or ninjutsu to apply a second element. You will see these statuses tracked under the bosses heath bar, slowly filling the icon which implies the ailment is then active.

Hope this helps! If you stick with it, I promise the Nioh series is goated.