If you use anomalies and outliers as your reference, you aren't conducting any scientific method, just biased opinion.
The overwhelming majority of players are much larger
Well if you are using the larger sample, there were actually some interesting discussions and data shown this playoff on how small players fare in the playoffs compared to how good they are normally, and then did the same for a similar range of large players. Turned out that both groups were virtually equal in that regard, both seeing a slight decline in performance. So if you actually isolate the factor and measure it, the results are not statistically significant.
Yes, most players are larger. Size, and the advantages it brings, is a tool, and we are talking about the best league in the world. If you set a generalized baseline and look at skating, most players in this league are great. If you do that and look at shooting, most players can rip it. That doesn't mean that a player without great skating or a strong shot can't be effective, it just means they have to make up for that elsewhere. Same with size. And in all these cases, the only thing that really matters is the sum of what they can provide. Therefor, it only makes sense to look at that sum for judgement and not just individual parts.
What I mean with that is that I don't understand how we can waste so much time talking about size in a vacuum instead of asking ourselves if someone like Robertson was the best guy available despite his size. And given what kind of prospect he is, I'd venture to say that he is.
