Regarding the dana-paramita (although the quoted MPPS section does not mentioned it) here is a little explanation from Dazhu Huihai:
Q: Where can one enter the doorway to this understanding?
A: Through the perfection of charity (dana-paramita).
Q: Buddha has said that the six paramitas are the action of the Bodhisattva path, so how can we enter the doorway to this understanding by practicing, as you have said, only the dana-paramita?
A: People who are confused or deluded do not understand that the other five paramitas all evolve from the dana-paramita. Therefore, in practicing the dana-paramita, one also fulfills the practice of the other five paramitas.
Q: For what reason is it called the dana-paramita?
A: "Dana" means the perfection of charity.
Q: What things can be given up in the name of charity?
A: Clinging to thoughts of duality can be given up.
Q: Just what does this mean?
A: It means to give up clinging, in the name of charity, to thoughts of good and evil, existence and non-existence, love and hate, emptiness and fullness, concentration and non-concentration, pure and impure, etc. In the name of charity, give up all of them. Then, and only then, can you attain the stage of the voidness of duality, while, at the same time, letting neither a thought about the voidness of opposites nor about charity arise. This is the genuine practice of the dana-paramita, which is also known as absolute detachment from all phenomena. This is only the voidness of all dharma-nature, which means that always and everywhere is just no-mind. If one can attain the stage of no-mind everywhere, no form will be perceived, because our self-nature is void, containing no form. This, then, is true Reality, which is also called the wonderful form or body of the Tathagata. The Diamond Sutra says: "Those who have abandoned all forms are called Buddhas."
It has already been pointed how the realization of emptiness of a first stage bodhisattva is identical in content to the realization of emptiness of a Buddha. But surely you admit that there is a difference between a first stage bodhisasattva and Buddha. If there is no difference in terms of the nature of reality, what then do you think the difference is?
The two accumulations of merit and wisdom are present in the mind. Emptiness is wisdom, function is compassion. Zen affirms that the trikaya is present in the nature of mind, so it is not that one has to develop wisdom for the dharmakaya and merit for rupakaya, but the buddha-mind is already perfect in all aspects. Still, that doesn't deny that there is also a gradual path of the bodhisattva, however, the gradual path doesn't deny the existence of a sudden path. Thrangu Rinpoche says that on the sutrayana it takes a long time to achieve buddhahood because they use analytical-conceptual meditation but Mahamudra uses an experiential method of directly looking at the nature of mind. A similar argument could be made in the case of Zen too.
Mahāmudra is part of secret mantra. Since the methods of mahāmudra do not exist in Zen, a similar argument cannot be made.
This might help better understanding, here is Zongmi's differentiation between the five dhyanas, that is, the levels of practice:
5. Direct (sudden) realization of the essential purity of ones own mind, originally without defilements, itself endowed with the influx-free (non-afflicted) gnosis - this mind is Buddha, ultimate with nothing else beyond - cultivating in this manner, is the Supreme Vehicle Dhyana. It is also known as the Pure Dhyana of the Tathagatas.
This is no different than the realization of a first stage bodhisattva. What then is the difference between a Buddha and first stage bodhisattva? You have still failed to answer this point.