Good catch!
It’s old news.
Boomer was buffed in Version 1.12 (May 2018) and Version 20 (March 2019):
I’ll edit it in the top post, and have let @Lumi know to update the database and image.
Maybe, but I think people are familiar with Boomer from experience and/or having him, since the last buff was a year ago — and I think the poor ratings accurately reflect even his buffed state.
As one of the very first Event Heroes added to the game, he really hasn’t aged well. He was a bit lackluster to begin with (thus being buffed twice), and has been very thoroughly outclassed by many of the 4* added to the game since.