I will never understand why Oda gave Lucci that beard.
Hopefully CP0 show off. It's been 2 years and some months, Lucci being comparable to Commanders shouldn't be too weird, he was a prodigy, plus spent years(?) undercover for a single mission (this is to say, rather than actual combat missions, he was just working as a shipwright yet still miraculously managed to grow even then according to Jyabura), I'd expect him to grow after recuperating from Luffy's beatdown and being promoted (for some reason) to CP0. Kaku too though I see no reason for Kaku to even be above guys like Jack, would be a bit much.
Overall, since timeskip, CP0 has had clashes with the likes of the Blackbeard Pirates and such so I don't think Lucci being strong or improving is so wild when his potential is one of the most highlighted in the series and Luffy is so far ahead now.