Disagree with that statement
Team cohesion is area that helps in preseason training to gel your team, when you sign/sell. I wouldnt say, that is teamwork the same...it is big difference, that the first one is general training and the second one is match training. Teamwork help to make your team to work as strong unit...the more matches that they play together, better they are imo. I dont see a point to focus on tactics, when tactic is fluid, so when they understand your philosophy.
About general training...like you said, mental attributes are the most important stats in tactic, so it would be benefecial to work on mental attributes through general training and through individual training focusing on role, that they play. Balanced training is pretty much default, which lead to gaining all attributes, but would be much better to focus to specific attributes, that suit to tactic.
This my view...cheers