It depends what you mean. Joshua can continue to make big paydays without Wilder, but Wilder is clearly the biggest fight at HW for him except for maybe Fury (and Wilder will bring more attention from the American market which might pay off for him more in the long run), and he offers the possibility of a unification (being the unified champion of the world will definitely help Joshua). So it's not really essential for Joshua to fight Wilder if all Joshua is concerned about is continuing to collect big paycheques, but the payoff of fighting and beating Wilder is substantial.
He needs Wilder and vice versa. He also need to beat Parker. You can't last forever fighting bums or the fans will slowly go away.
No matter how huge AJ is, he knows and said it himself to be a worldwide superstar you have to make it in the states. The money also better if you become a US ppv star.
Joshua and Wilder are the consensus #1 and 2. Which will be reinforced if they both win their upcoming fights.With a Wilder fight in sight? Where does Wilder draw?
Joshua.
I think he will be too big and strong for Parker, who I think will have a swarming strategy, but with not enough of a big punch or defensive skills to trouble AJ, so he'll get picked off and stopped late.
Also, a potential contender of KOTY will be on the undercard with Alexander Povetkin vs David Price. Hearn could be selling the UK audience as a future AJ challenger.
http://www.bbc.co.uk/sport/boxing/42722532
I'll be watching this through my fingers, awaiting the inevitable.
Why? People made a big deal about Takam giving Joshua some issues, but Takam arguably beat Parker (same with Ruiz Jr.).