I don't think it's as simple as "mining centralization would not be a problem anymore" but it would at least be a smaller problem
Stratum V2 is a more open source altenative to datum. Both do the same thing but datum's server code is not open source yet, and consequently only one pool is running it (Ocean).
Even if SV2 was the norm, it would still be bad if there was a very small number of pools, because there is an unsolved problem which neither SV2 nor datum solves. And that is, the pools running either one can stop responding to you if they don't like your block templates. If that happens, your main option is to switch to another pool running SV2 or datum. If none is available, you can run your own pool, but that's already an option right now and those protocols don't really make it any easier
