Yup, yellow card is definitely too small penalty.
I was thinking of giving 1 match ban after 2 or 3 yellows instead of 5. It's much easier to implement than sin bin, although sin bin has direct impact on the game foul was made, so if implemented correctly it could be better.
That's a big if though
I've watched a few of his Bayern goals and it looks ridiculous. He's just jogging around the pitch and scoring for fun, doesn't seem to take much effort from him. Looks like he's head and shoulders above bundesliga level. He should come to premier league to really prove himself now ๐