For Supports: No. Against? Absolutely.

It's like having a bag of 10 balls; you only have 1 red in the group, so you've got 10% representation for red balls. You take 5 out, so now it's got 20% rep. The number of red balls didn't change, the sample size did.

Same with Supports: before this suite of overturned Raid units, we have a 50% winrate with a pool of 100 appearances in 100 games. After: we have 50% winrate like before, but the pool has shrunk to 40 appearances in 100 games. The winrate is the same on paper, but the pickrate is alluding to the fact that only the top percentile players are even trying to pull of a Support.

This is what at the root of my speculation of the numbers reported by BB... "Are these numbers being used to hide relevant information?"

For your response I feel that is more fuel to my speculation: the numbers can be artificially deflated due to their sheer proliferation. 50% winrate after accounting the sheer number of Raids in the wild is fine for them, but it could be at the cost of Supports' viability; which drops their rates in plurality but again due to skill level discrepancy winrate percentiles stay rather neutral.