More tactics or more games?

He is right, for sub-2000, you should not be reading loads of opening books. Just do tactics to reduce blunders and get the patterns in your head. I would also advice that you don’t play blitz. Play classical and other longer games like correspondence that will allow you to think through each move.

I improved from sub-1000 to 1800 just by tactics and reading a few introductory books like those for Yasser Serwan and Silman.