Comment by woutifier

Defense against rainbow tables is obtained via salt, not via slow hashes. A rainbow table is a space-time tradeoff (you give space, and you get time), so using a slow hash only "encourages" (for lack of me knowing a better word) creating rainbow tables.

Adding long salts on the other hand requires the attacker to create an infeasible number of rainbow tables (one for each possible value of the salt).