The increased amount of training materials online has led to a massive overall improvement in standards. This is particularly so at NLHE.
Edges are now really small and completion of one training course does not guarantee making you a winner.
You have to keep working and put in significant volume if you want to turn your edges into profit.
Some of Polk's recommended weak 3bet hands are imo definitely suspect.
For example if you are polarising your 3betting I don't recommend using his suggested small suited 64 75 type hands. Typically they only have 20%
equity when called. You should use suited kings and Queens which can still out flop a hand that will call a 3bet like 88-JJ with around 30% equity. Over time that extra 10% will add up.
Generally most of the material I've seen from him is sound especially the post flop stuff.