There is something that you need to fix here. That is the role of the deacon. The deacon is not the second choice to distribute communion. The deacon, is an ordinary minister of the Eucharist, because he is a cleric in Holy Orders. The rule that governs the deacons, since the time of the Apostles is that the deacons were ordained for the benefit of the bishop, which the Apostles were.
The custom was that the bishop would consecrate and sit. The deacon would distribute the Eucharist. This custom is still in use in many Eastern Churches where they kept the permanent diaconate, as well as Orthodox Churches. It is not that the priest is the first choice to distribute communion. The first choice is any minister ordained to any of the three orders of the priesthood: deacon, presbyter and bishop. That’s why the other are called extraordinary.
As to communion on the hand vs the tongue. This is only a debate in the West. In some Eastern Churches this has always been the case, They are just as Catholic as we Latin rite folks are. There is no universal rule on receiving communion. That’s why it was permissible to grant an indult. Because the method is, as you rightly said, not a matter of dogma, but of discipline. But this discipline is determined by each Church, not by the Holy See for the Universal Church. The Holy See allows each Church to act according their rite. In some rites they use spoons so they can dip the host in the chalice. In other rites they pour the consecrated wine over the consecrated bread, making the bread very moist and then they distribute it with a spoon. In other rights they hand the communicant the consecrated bread and then the consecrated wine. In mos rites, the deacon distributes communion, not the priest or the bishop.
Remember, each rite has its own canon laws. The canon law that we know was written just for us, the Latin Rite Church. There is an entire code of Canon Law for the East. In that code, the Eucharist may be distrubuted on the hand without an indult and the regular minister is the deacon, not the priest. They are just as much Catholics as we are.
Our debate about the communion in the hand vs communion in the mouth and our debate about the deacon vs the priest offends the Eastern Catholics. Because they feel that our way of talking makes it sound as if they are doing something wrong or less reverent, when in fact, their rituals and customs are just as old as ours and just as apostolic, not to mention, just as Catholic.
We have to be careful how we discuss these points to always make it clear that we’re not talking about Catholics, but only about Latin rite Catholics.
Fraternally,
Br. JR, OSF