...tactics are fundamental to success, there wouldn't be the need for the constant re-invention of the game in order to gain that upper hand!!!
Manchester City have achieved success due to how they play, the ability or inability of their opponents to overcome what is before them and the quality players who implement the tactics.
Did they need Mahrez, I do not think so, It had two advantages to bring him in, firstly it was a proven player who could play the system that they wanted and had the ability to outwit a defence, and secondly, it took Mahrez off the market weakening potential rivals. Football has elevated itself to chess, someone just needs to come up with a certain different approach to render current convention outdated.