Zoro's character and fighting style is too dominant to let him loose.
This is what happens when Oda lets him loose too early
On FMI he no diffed the frog guy who was on the same drug as Hody and who was explicitly stated not to be his subordinate but a freelancer
On PH he wasn't allowed to be anywhere near Ceasar or Vergo (I wonder why...)
On DR, Oda used an admiral to keep Zoro away from Doffy.
Later Zoro was stalled for 20 chapters with the fodder Pica and his hide and seek game. The moment the plot needed it, Zoro destroyed him low diff
On Wano the bro showed superiority towards Hawkins, Apoo, Drake, Law (by extension since he extreme diffed Hawkins)
On Egghead he wasn't allowed anywhere near the VAs. Lucci who is the closest one to Kizaru on the island was used instead to keep him away from the main happenings on the island. The reason is clear.
With zoro at the main scene we wouldn't have had
- 25 staring competition chapters
- VP getting brutally mutiliated in front of everyone
- Saturn bullshitting endlessly and keeping Bonney hostage
With Zoro at the main scene we
would have had