Playing TIE,Normal or CT does not affect the ratings but affects the way your team plays that game. The enthusiasm that you have (numerical value) affects the defences and the rebounding.
If you play TIE your enthusiasm raises 33% but it will always gravitate to 5. If you play Normal the enthusiasm will not change, only with the daily update (don't forget, always gravitates to 5). And if you play Crunch Time your enthusiasm will be cut in half.