People will argue Crosby’s the best in the league until the year he retires. He was/is an incredible player but some people just can’t accept the thought of another player being consistently better.
Crosby is still the #1 player you take for playoffs. That's why a lot of people still argue that he's the best in the league.
If McDavid had qualified for the playoffs each of the last 2 years, and performed up to expectations based on his talent - I expect the support for Crosby would be a
lot smaller. I'm not blaming McDavid here - just stating that if he had done that, people wouldn't answer "Crosby" to the answer of who you take first for a playoff series today. As it is - Crosby's experience in the playoffs gives him benefit of the doubt over McDavid for many fans still.
Should McDavid go on to make the playoffs this year, make it to say ~round 3, and score something like 28 points in 21 games - if you redid this poll next year i don't think many people pick Crosby anymore. (of course - if Crosby himself outdoes even that, and maybe wins a Conn Smythe, that might continue).