IDK the sample size but it needn’t be very large for meaningful data. Whether say a 70% rate is accurate within 1% or 10% doesn’t really mean much in this instance. If the Indian variant is 60% or 80% of cases, it’s still clearly the dominant strain it seems to me.
I suppose you’re right, unless one or more of the “vaccines” are less effective against a particular variant. Data out of Israel and the UK isn’t very encouraging (Pfizer and AstraZeneca, respectively) against Delta variant. Still seems somewhat effective but not as robust nor lasting. Israel says Pfizer is only 39% effective but still reduces serious illness by around 90% or so. AZ vaccine seems the weakest (compared to the 3 we have here, not sure about Russian/Indian vaccines) but the UK/EU had to take what was available at the time.
I read that in the UK, 40% of hospitalizations are among double-jabbed with the AZ vaccine... not good.