Overbuff was also biased. Specifically, towards high ranked players. We know that clearly because the player distribution per rank in their database is much higher than the official numbers.
But even then, Overbuff sample size is at least one degree of magnitude higher than any random strawpool you can gather about role queue. So while the data is biased and should be taken with a grain of salt, it’s still a large pool, which means higher chance to reflect reality.
Also, Overbuff collected empirical data. Strawpools are subjective feelings that can change over time. So what was true about those pools before role queue hit live might not reflect reality after one month of role queue on live. Many people might have changed their opinions (for either side), and we need to get another sample to see how public opinion evolved over time.
(Which is why election pools are made during the entire duration of a political campaign, instead of only once at the start)