A trick I was shown many moons ago ,which has NEVER been known to fail in over 30 years -
You use two hammers , one a small sledge and the other is a 2lb or slightly bigger ball pein .
Slacken off the nut most of the way .
Place the large hammer behind the tapered ball joint female part , touching it and apply enoough pressure to hold the hammer in place .
Whack the ball joint "female part " with the smaller hammer directly opposite the large hammer .
You might have to give it several blows ,but the ball joint tapered part will pop out of the tapered female housing .
What happens is the large hammer acts as an anvil and the smaller hammer blows cause the female taper to distort slightly and break the "seal".
This method is extremely useful if you want to dismantle the joint without damaging the rubber cover .
It is obvious from your photo that whacking away willynilly on the arm did not work and in some cases could cause damage to the steering arm .
You simply do not need brute force to separate the parts and you should never beat on components like that .
If it's a fight - you're doing it wrong .
When you refit , apply grease or copper coat to the taper .
Hope this helps .
Blessed are the cracked, for they let in the light. - Spike Milligan
"When you come to a fork in the road ,take it ! When you come to a spoon in the road ,take that also ."