First, your numbers are off. The 2014 data blizzard gave us showed 0.5% of players made legend.
https://playhearthstone.com/en-us/news/15955974/hearthside-chat-youre-better-than-you-think-9-18-2014?
Then, last November, they gave us an update which showed making legend had become harder, not easier, at 0.3% of players.
https://www.hearthstonetopdecks.com/end-of-month-players-rank-distribution-in-november-2019-0-3-in-legend-6-at-rank-5/
As for April, there was a combination of first time incentives, a huge influx of players, and a lot of people spending all of their time at home.
If we ever get data on this particular month, and I don’t see why we would, I don’t expect the percentage of legends to change much.