Argument is valid. Yet it takes no step in the direction of describing how, or in what actual concrete form, perfection is realized. The categorial or logical gap between essence and existence, which Henrich stresses, in the divine case becomes an absolutely infinite gap between abstract essence and/or existence, on one side, and concrete actuality on the other.
The trust in mere dichotomies was effectively criticized by Peirce seven or eight decades ago. But the lesson has yet to be learned. The 'cultural lag' in philosophy is great indeed. (Thus Henrich in 1960 does not know Prosl. III.) 'Existence' can have various positions short of full concreteness or actuality, but in one supreme case it must be as abstract as essence, and hence a priori. The comprehensive or universal contrast of idea or essence is with actuality, not with existence.
Against these authors I maintain: Anselm discovered, and really discovered, the modal uniqueness of the idea of God. What he overlooked, and nearly all his critics equally fail to see, is that, since actuality cannot be necessary, there must be a real duality in God, as in no other being, between necessary existence and contingent actuality.
There is a final consideration. Philosophers all know that according to Kant the other supposed proofs for God fail unless they can resort to the principle of the ontological proof (that perfection and necessary existence are inseparable). Kant is believed to have refuted the principle, hence to have disposed of all the proofs in one blow. But did he refute the principle? True, he also accused the proofs of other weaknesses.