Lol, never once Lucci said anything about that after the fight. It was pre-fight and Lucci using it an 'excuse' to fight Luffy.
Also, Lucci started fighting as soon as Luffy went away with Franky by your logic.
Also, the logic apply because Luffy said not to take out his anger on his crew mates just because he can't beat him which is exactly wat he did as soon as luffy gone.
Again, he didn't say 'now I know why Luffy is a yonkou' or 'I admit Luffy is a yonkou' but he said 'no.2 of yonkou' which means Luffy is already an yonkou in his mind and it is worth if he can take out no.2
Also,
Lucci: no. 2
What Lucci said in the mind of Guy with Einstein IQ:
Lucci with terms and conditions: You are no. 2 bounty wise and no.1 strength wise and Luffy is a figurehead yonko, you are real yonko.