@Audity:
Was thinking before or at the start of watching: maybe they could bring back some staff from the origins of the anime by the time One Piece is finally at its finale. And then I was pleasantly surprised to see that this episode overall felt like it could've been from that time (even with pacing mandating such little chapter usage). (I'm also feeling much healthier from sudden malaise/problems forcing max hydration + detox of energy drink/caffeine/chocolate/anything for weeks now, coincidentally!)
I've never researched any staff (besides the usual musicians), though, so I have 0% idea what I'm talking about—other than that I remember people saying that a whole bunch of people were fired by the time One Piece went widescreen? No idea if some staff still comes back from that era in modern times, or if some of them are permanently gone for a reason or another. Still, would be really cool if any circumstances allow for the finale to have as much of the original staff (if it would make a difference anyway?) as possible. These thoughts just fill me with memories and possibility, regardless.
There was no real firing. Yes, the series director changed, but for the change to wide screen? Nah.
Several of the regulars of the show currently, especially in the animation supervision department, are staff members that have worked on the show pretty much sense its inception. Hell, one of the two animation supervisors for this episode made his initial debut on the second episode of the show(and has handled several well known episodes in his role, such as Zoro's sacrifice episode in Thriller Bark, or the death of the Merry in Enies Lobby), and the animation supervisor for next weeks episode literally worked on episode one.
Considering that One Piece is a show that has gone on for 20 years, staff(animators, animation supervisors, episode directors, series directors, storyboard artists, character designers) come and go not infrequently in the vast history of the show for a variety of reasons. I remember the original character designer for the show left sometime during Thriller Bark, apparently due to the workload associated with the role, and other animators usually go on to do bigger and better things.
With that in mind though, a lot of animators who have worked on the series for extended periods of time and have left, do have a history of participating again on the franchise in some capacity. For example, there are a lot of One Piece alumni animators who have a long history with the franchise, who worked on movie stampede.
With that in mind, there are still some animators who have either consistently worked on the show for 20 years, or have consistently returned to the show, who worked on it during its conception. For example, the animation supervisor for next episode, Masahiro Shimanuki, left for the show to work on DBS, and returned once it finished. Also true for the guy who animated Luffy's storm against Crocodile, Rifle against Enel and Jet Gattling against Lucci(all animated by the same guy), who left the show for the majority of Dressrosa, but returned halfway through WCI, and is still working on the show.
In saying that, new staff is definitely not a bad thing. Having fresh talent on board, even if just rookies, and giving them the opportunity to develop and improve their skills on the show is a definite positive.
P.S.
Mentioning the first character designer for the series, although he left during Thriller Bark, he actually did return for two episodes of WCI, 808, which was Luffy vs Sanji, and 816, for Pedro vs Tamago. His currently working on Kitaro.