In general it is is not true that Argon2 should be recommended over bcrypt. Even even some of the people on the experts panel for the PHC (where Argon2 won) won’t recommend Argon2 over Bcrypt: https://twitter.com/TerahashCorp/status/1155129705034653698

Looks like for the typical case (~200ms calculating the hash) bcrypt beats argon2. I guess that’s what I understand from those discussions, I’m not an expert by any means. It is related with cache hardness: https://twitter.com/Sc00bzT/status/1149963675069026304