Kizaru likely is depressed and all but powerlevels aside it just sucks for Oda to do this to him. First chance we get to see an admiral all out against other top tiers and it's wasted on this depressed cog jobbing around.
It's not enjoyable, I want to see him fight properly, nerfed or not.
As it stands, why bring him in the first place, right?
It could've been Lucci + Saturn alone and it would've been enough. Bringing Kizaru, throwing in this mentally unstable mess and have nothing come out of it would be horrible writing which I why I think Kizaru must betray the WG.
With VP saying to Dragon that there are good people in the Navy Oda may have worked towards this.