Your stat on the reach of InfoWars is based on claims from 2017, before the de-platforming. More recent reports point to considerable slumps, eg: https://www.nytimes.com/2018/09/04/technology/alex-jones-inf...
Voat is discussed elsewhere here, too. In short, the point was precisely to get the speech off Reddit because it was poisoning Reddit. People said it wasn’t worth them trying because it would move to other subreddits. It didn’t, it moved offsite entirely.
De-platforming worked for Reddit. OP asked for tech contributions to reducing the amount of polarised speech in online spaces. There is one.