Haki is One of your Stats, same as Strength or Speed ... etc
Lot of DFs also mainly Improve your Stats or simply provide a Weapon for you to Use,
But what matters is your Fighting-Style
Do you have a DF-Based Fighting Style or Fighting Style based on something other than DFs,
Also most have a Single Fighting Style but some can have Two,
You can also have a Fighting Style that is based on both DF & Haki,
You can determine these Fighting Styles by simply checking these Character's Signature Techniques,
Examples:
Jinbe have a Single Fighting Style that is neither based on DF nor Haki,
Shanks have a Single Fighting Style that is based on his Haki (CoC),
Akainu have a Single Fighting Style that is based on his DF,
Luffy have a Single Fighting Style that is Combination of Both Haki/DF,
Sabo have Two Fighting Styles, One is Haki-Reliant (CoA), Other is DF-Reliant,
Kaidou have Two Fighting Styles, One is Haki-Reliant (CoC), Other is DF-Reliant,
Blackbeard have Two Fighting Styles, Both are DF-Reliant,
As for their Ranking,
Low Top Tier ---> Requires 1 S- Fighting Style (Such as Ace)
Mid Top Tier ---> Requires 1 S Fighting Style (Such as Akainu) or Two S- Fighting Styles (Such as Sabo)
High Top Tier ---> Requires 1 S+ Fighting Style (Such as Shanks) or Two S Fighting Styles (Such as Blackbeard)
This means aside from Blackbeard, you cannot reach High Top Tier except with Haoshoku Haki,
Either by Itself (Like Roger/Shanks) or Using it to Enhance your DF (Like Sengoku/Luffy) or have Two Fighting Styles (Like WB/Kaidou)