I actually think the filler between Skypia and the Foxy Pirate thing is very very good!
It's about the strawhats dropping directly into the middle of a marine base and gets split up, so they have to go undercover in this marine base and try to make it out alive.
Of course most of them gets caught eventually and has to get themselves out of the vipers nest they are inside of, and well, get their ship to.
I really love that filler arch because strawhats that usually don't get to do certain things they have been established as being able to do.. but just doesn't, they get to do it here.
Sanji gets to teach a bunch of marines how to cook and appreciate the value of food.
Robin gets to go compleately cool and calculated under cover pulling their asses out of the fire.
Usopp gets to tell a very useful and clever lie to bluff them all out of trouble, as well as getting to make a well thoughtout retrieval plan they all listen to and follow.
Chopper gets to be a doctor, teaching another doctor the worth of her profession.
Nami gets to retrieve some of the others when things go wrong and be smart.
It's a very enjoyable fast paced little filler arch with lots of great character stuff, genuine build in foreshadowing for the water seven arch, good character moments and character interactions.
It's so good I was extremely surprised when I found out that arch is in fact NOT in the manga! Because really it's just such a nice little piece of fresh are allowing the character to just be themselves, running around showing off what each of them can do.
