I think Kidd was stronger up until Luffy fought Katakuri. That's when Luffy really started to take things to another level, and was able to fight strong opponents in base.
Right now, I think Luffy, Law, and Kidd are similar in power, as all three of them need extensive help to be able to beat top tiers in a serious fight.
Kidd and Law are shown as Luffy's equals for a reason by Oda.
Kaido took a ton people to take down, but was knocked out by the end of the fight, while Big Mom fought way less people, but fought two Captains on Luffy's level, Kidd and Law, for a long time, and unlike Kaido never went unconscious on panel.
Luffy has better Haki, and stronger forms, but his strongest forms from his Fruit leave him vulnerable. Law and Kidd have worse Haki, but their Fruits don't leave them vulnerable like Luffy, while also not being able to do as much damage as Luffy's Fruit.
All three are worthy of their current Bounties.