I don't understand or know about how pools can integrate stratum v2 but if it is possible I wonder why did ocean not launch with stratum v2 right away?

There are plenty of small pools that sign blocks/create block templates other than the big ones. The big pools are just the ones finding blocks. If they collude, they still don't control the hash and miners can effortlessly point to a small pool like kano pool. Kano pool for example went over a year before it found a block and now it's been several months since the last block they found. Kano is an example of where hash can go if the big pools start colluding. Hash is concentrated to a few large pools but not under centralized control. 

 There are 2 questions here:

1. Why not stratum v2 right away?

I'm not an expert, but maybe miners need to upgrade their firmware? Well, some sort of software upgrade must happen, maybe they are not ready?

2. Why not Kano pool?

Miners seem to prefer FPPS to other payment schemes, which makes sense, due to the steady stream of revenue. Since Kano only finds one block per year, I don't see how it could offer FPPS to its "customers", so in that regard Kano pool will always be behind bigger pools. So, in this particular question, size matters 😉

Again, not an expert, just thinking out loud.

https://originstamp.com/blog/pps-vs-fpps-vs-pplns-vs-pps-mining-pool-payouts/