Was Fishman Island Arc Jimbei's power a retcon?

[Captain Cadaver]

At Marineford, Jimbei was hyped up and portrayed as being pretty high tier, being stated to have been an equal to Ace and managing to block and endure an attack from Akainu with the full intent of killing Luffy. On Fishman Island, he tied with Gear 2nd Luffy and the fight with Wadatsumi suggested Sanji was in his league. Then on Whole Cake Island, Jimbei's back to being portrayed as high tier, managing to knock an off-guard Big Mom with his best Fishman Karate techniques and block hits from her with Busoshoku Haki.

So, would you say Jimbei's strength in the Fishman Island Arc was a result of the arc's generally bad writing?