The answer is quite simple and nothing too weird is happening.
Your hero is mounted (cavalry unit), legionaries are on the other hand infantry.
Even though your attack nearly doubles because of the addition of the legionaries 5000 to 9000
The defense of the clubs raises from 5000 to 11600 because of their significantly higher infantry defense (20 vs 5)
If you add equivalent attack in cavalry instead (33 EI's) you will see the fight turn very one sided instead
So when i atack with infantary the defence to infantary is the defence of the battle even against cavalary units?
It's not quite simple.
Basically what happens is that the game counts up the total attack coming from infantry and coming from cavalry
In this case it would be 4000/9000 -> 4/9 infantry and 5000/9000 -> 5/9 cavalry
Then it takes these ratios and applies it to the defense units. In this case the clubs will defend with around 44% using their infantry ratio and 66% using their cavalry ratio
In this case 1000*20*4/9 + 1000*5*5/9 = 11669 + 10 (from village base defense) -> 11679 which you will see in the simulator
Ok i think i got it now i didnt know the battle was about pecentage. Thanks this is a realy usefull information