I personally am not one for paying attention to polls when it comes to rankings of the BRF because I don't think a large enough number of the population is taken into account. Besides that I don't think the Duke and Duchess of Sussex need the click bait for people to be interested in what they are doing. They are non working royals and live in America.
You don't need a "large" number of the population. If you use proper random sampling, it is possible to estimate Harry's rating within a margin of error of +/- 2 percentage points and a confidence level of 95 % with around 2,000 people only.
The key is that, in your random sample, you must be able to draw any adult person in the population with equal probability.