You are right they aren´t fighters, but this didn´t held Oda up from giving them 1on1 or 2vs1 battles in Alabasta,Enies lobby, two big arcs.
So they actually show such things, Usopp as example had also 1on1 fights, Luffy vs Usopp was one of the greatest battles between a strawhat member.
And you said it, Nami get Zeus and Usopp get haki grow in DR.
Since that I was hoped to see how they growing up with their new learned ability.
This is a arc of 400chapters of build up, for Nami and Usopp it would be important to let them grow up in this battle, going over their limit like we see in Alabasta or Enies lobby.
And their opponents where get is really worse,Pageone literally not have any move attack, Ulti just use one attack(named one) and the second one was never used...
For all four characters, such a rushed battle is really disrespectful, Nami and Usopp fans wait for so long to get this?
It was not just her weapon, she basically did it on her own after a brutal battle, a great one with good tension, great cheoraphy and good artstyle overall with a great enemy for Nami:
These are the panels before she use the weapon, she did it on her own power, stop the attack with taking a painful attack.
Overall should I showcase the whole fight again? Just compare the fight with Miss Doublefinger vs Nami fight with Ulit..
Full fight with Doublefinger for these one who actually forget how much time and insane work Oda did with the past strawhat battles:
That was Nami first big battle on her own, a battle who had anything.
Gag scene, Nami as character growing, as fighter growing, a good enemy with interesting moveset, cool attacks from both side, tricks like Nami making illusion, a very hard battle for Nami where she go over her limit, where she himself need to put the work in the end.
Great artstyle, a full fight who take over 4 chapters next to next, Oda make a great set up and end a great battle.
Same with Kalifa, Oda spend at least chapters and good battles.
Where both villian and protagonist show skills and interesting moveset, great matchups.
And now compare that what we get in the past with Ulti and Pageone vs Nami and Usopp...
Pageone barely show anything, dude has legit not shown any attack, Ulti had just one move, something liike interesting moveset with different skills in new world where haki and df can play a big role and all what we get is this?
I going to debate with anyone who wanna try to say me that Ulti+Pageone vs Nami and Usopp is actually a great battle, it isn´t it. No tension, no feeling, running over running, offscreens... Missdoublefinger show more then Pageone+Ulti did together.
And we wait 400chapters,10 years of hope for Nami to get again a real good battle, but nope, Tama is more important, Tama is actually stealing the show of the strawhats(even Ulti pointed it out this chapter lol).. The strawhats who let start us to read this manga get threat like side characters while side characters actually get threated better with far better panels(Scabbards) or Tama who has right now more screentime then King,Jinbe,WsW together....