Wano's length actually scares me for what's coming lol. You have 5x the characters (2 Yonko, Revo's, Marines/WG, Vegapunk/Kuma, etc) who are as or even more important than Linlin or Kaido. You have concepts like Rocks and Im that haven't been fully introduced. Factions like the Underworld or Level 6 escapees unaddressed. You have entire islands not visited yet. You have missing road poneglyphs and MIA characters on the side.
Like if BM is in Elbaf and Elbaf features anything more than her (i.e. Vegapunk or Urogue or Bonney/Kuma or Revos), that arc alone will probably clock at 100 chapters at least. Does Laugh Tale have a villain? Then it'll be decent length and not "short" like people expect. Lodestar? God Valley? Another island we don't know about yet?
And remember, if villains or characters aren't addressed prior to the final war (Elbaf, Lodestar, Laugh Tale, etc), then it ONLY makes the final war bigger.
Tldr: 5 years left was a complete and utter fucking lie lmao, even if you just tie it to Luffy's journey to PK and not the Final War.
I really don't think he would have the usual problems.
I think all out war scenarios are relatively easy to handle. You can distribute all those different factions on to the WG hot spots, where just a limited number of the highest ranking WG officials and Marines + fodder awaiting one specific alliance faction and then they just go all out on each other.
If Oda would now write how Mihawk vs the Marine fleets went down, he could easily put it into 4 chapters max. Or just take a look at Scabbards+Oden vs Kaido+King and Queen. Go into detail and you still only need like 10chapters for it to be sufficient, if those aren't main arc fights, where the protagonists unlock PUs and stuff.
There likely would be no damsel in distress themes, no "underdogs secretly working their way through the island's regime"-kinda plots. I can even see top tiers agreeing to switch to specific battlefields for going all out. A lot of very isolated top tier fights will most likely happen.
Then you also have to think about how the biggest, non flashback lore- info drops only take like a few pages to be fully covered. Like Robin reading the last Poneglyph or Vegapunk explaining the DFs' origin would just take a few pages each, even if those are two of the biggest mysteries left in the story.
If Laugh tale doesn't come with a conflict and they really just enter the island and find the one piece, it could last 4chapters and it would be sufficient for example.
Imo Elbaf could likely be the last arc, where one of those usual major underlying themes will still be prominent.