Not necessarily, Haki was necessary to A. Touch logia users and B. Diversify combat in tha manga. Without it, we’re left wit tha stronger or strongest characters being people who got exceedingly lucky in life and everyone else being bland or unlucky wit no way of evening tha playing field out. Haki was necessary do cull this
What Oda HAS failed at to this point, is explaining Haki and its limitations. As well as tha consistency of Haki(all 3 types). Perfect example, Luffy is a FS user yet still gets snuck up on and surprised, tho CoO is THEE most inconsistent ability in tha manga