Must be because Oda plans to have Zoro "master COO" mid battle in order to beat Shiryuu. Seriously this fruit is borderline useless against top tiers since most of them have good COO.
I cannot fathom why Shiryuu gets this fruit over tons of much more useful fruits for pure combat. Sure its nice for sneak attacks against guys who don't have high level COO but thats it.
So far Zoro has good COA, just started using COC but he lacks COO feats. Most likely his COO is still on the weak side so this makes sense to me.
And oda has shown that he has no problem with guys upgrading haki mid battle.
Bruh, Zoro's CoO is better than Luffy's, it is fully mastered. He is doing better with basic CoO than Luffy with FS.
Just because he doesnt have FS, like 99.99% of people out there, doesnt mean his CoO isnt mastered...
There is no mastery of CoC, it is on or it is off. The moment Luffy and Zoro coated themselves with it, it is mastered.
And the reason why Shiryu has gotten Suke Suke no Mi is because that is the best fruit a swordsman can ask for.
It looks lame because it is "just invisibility" but the fruit has never been about invisibility alone, it is about clearance.
It has already been hinted at what its Awakening will be - Indivisibility aka losing physical form.
That means Shiryu becomes nothing and any swordsman who cant cut Nothing is fucked.
Or any fighter that cant target him and since only swordsmen are rumored to be able to cut nothing, others are doomed.
For 99.99% of people out there, fighting Awakened Shiryu is like punching air, they cant do anything.