What!? He used it twice pre-skip. The first time was because he got pushed to his utmost limits by Kumadori, was reduced to a bloody pulp, and had no more options left available to avoid being killed since his other forms ultimately failed to Kumadori after a long and hard fought battle. The second time he used it was when Sentomaru, an admiral, and a schichibukai were dismantling the crew one by one and there was absolutely nothing the Strawhats could do about it. What part of that is him just trying to show off? The two times he used it pre-skip were the most dire circumstances in his entire career as a pirate.You've seen Chopper use it once Pre TS and it was just to show off.
Contrast that to post-skip where he enters the form to deal with Dosun, one of Hodi's chumps who he was already fighting on par with in Heavy Point alone. Using it to stall when he literally has another form designed for that very purpose. Now he's pulling it out on Noble Croc, some trash homie that never even threw a single attack.
I see no reason why he couldn't have taken Noble Croc in Kung Fu point; Carrot made the group look like a joke.Right now was the right time. You don't use Kung Fu or Walk to decide a situation like this.
You depend on ingenuity if you had time. They didn't have the luxury of waiting. Chopper's trump card is MP. They had to take them out before they could react fast enough.
If Oda is unable to create scenarios for Chopper to utilizes the other 6 forms in his arsenal, then that's a fault of his as the author. It's not good writing to establish a wide, varied, and creative arsenal for a character to work with, then have it all rendered completely obsolete by the one trump card he spams to get out of every situation.