Everyone should be $400,000,000 bounty or higher in the end, so yeah they all need to get much stronger. Which means everyone of them needs haki, right?
Most of them. I don't think Nami will get it because it won't add much to her fighting style. Usopp is weaker than her, but to be the best sniper he severely needed it. Though I have to wonder how Usopp will not surpass Nami because he's first and foremost a fighter, but for her fighting comes second. :/
The ones that have gotten the longest fights are Luffy, Zoro, Sanji, Usopp, and Franky. Robin and Brook have shorter fights but tend to finish thing quickly, or be support - which isn't a bad thing because Brook in recent chapters have been awesome and Robin's DF was extremely useful on DR. Chopper and Nami rarely have fights anymore(I'm haven't completely caught up to the manga though), so I think if everyone gets Haki it might happen in the order above, since it's often awakened when they're struggling.
My point was that they don't need to be monsters to have Haki, I think it's a fairly common thing in the new world, so they should be caught up. And vice admirals aren't that strong, all endgame SH's should be able to take on an average VA.
I've been wondering something btw if anyone understand, how could Jack swim back up after getting smacked by that elephant? In a recent episode he was on the bottom of the ocean but he survived. When Luffy sees seastone he becomes completely limb and I thought all DF users had that weakness..