Do people finish all sub missions and main missions?

I started playing Nioh 2 two months ago. I've done every sub mission, killed every enemy and looted all places since I've began playing, and only yesterday did i reach the third map (shadow).

I know that there are many maps. Is that how you guys played the game? If i keep doing this, I'll spend the entire summer playing Nioh 2. Is it okay if i just do the main missions?

Idk it just seems like it's really long and time consuming.