To find out if the early Christians universally assumed the Catholic doctrine of the doctrine of the "Real Presence" to be true then one should examine the only wholly inspired and substantive record of what the early Christians believed, this being the New Testament, and in particular, Acts thru Revelation, which reveals how they understood the gospels.
Rather than being manifest asc being the "the source and summit of
the Christian life," (CCC 1324) which is "the cause of that
communion in the divine life," (CCC 1325) and the work of our
redemption is carried out;" (CCC 1364) the Lord's supper (LS) is
only manifestly described in one epistle, that being 1 Corinthians
10,11, besides the reference to the "feast of charity" in Jude 1:12.
If the mention of breaking of break together in Acts is that of the
LS, then it is that the disciples who from from "house to house, did
eat their meat with gladness and singleness of heart."(Acts 2:46)
Rather than being "the same sacrifice with that of the cross...a
sacrifice of propitiation, by which God is appeased and rendered
propitious;” (The Catechism of the Council of Trent) it is nowhere
described as a sacrifice for sins, but a communal meals which
shows/proclaims the Lord's death for the church by unselfishly
sharing food in a actual meal, thus showing unity with the object of
that dedicatory feast, and each other, as did pagans in their
religious feasts. See here.
Rather than only a duly ordained Catholic priest being able to
conduct the LS, with the primary active duty priest being "most of
all to offer the Eucharistic Sacrifice," (Pastoral Reflections on
the Holy Sacrifice of the Mass, Cardinal John J. O'Conner) nowhere
do we see this restriction, nor even Catholic priests in the life of
the NT church, this being a separate class of sacerdotal believers
for which the distinctive Greek word for such (hiereus)is translated
as priests though it is actually a etymological corruption of the
Greek "presbyterous" = senior/elder) See here.
Rather than consuming the elements in the LS being a primary means
of spiritual nourishment that "gives life to the believer""the
irreplaceable food for the journey of the pilgrim church on earth."
(USCCP: "Norms for the Distribution and Reception of Holy
Communion," paragraphs. 4,14) "the food that makes us live for ever in Jesus Christ," (CCC 1405) so that after their first sacramental
confession children are to be "nourished by this divine food as soon
as possible;" (Can. 914)
Nowhere is consuming the bread and wine described as providing this irreplaceable spiritual nourishment. Instead, spiritual life is obtained by hearing the gospel and truly believing it. (Acts 2:38; 10:43-47; 15:7-9; Eph. 1:13) And which provides spiritual nourishment by drinking "the sincere milk of the word," (1 Pt. 2:2) and ingesting its "meat," (1Co. 3:2; Heb. 5:12,13) being "nourished" (1Tim. 4:6) and built up by the word, (Acts 20:32) and with feeding the flock thereby being the primary active function of pastors, (Acts 20:32) besides prayer. (Acts 6:4)
In addition, the NT church certainly did not subscribe to the claimed but actually metaphysical Eucharistic theology of the Roman Catholicism, that of the "Real Presence" (though that term was apparently originally Anglican), that at the words of consecration by a validly ordained priest, the valid bread and wine, entirely in each one and in each of every particle (down to the most minute one), no longer actually exist (the bread and wine have ceased to exist after the consecration" - Pope John Paul II, Ecclesia de Eucharistia, 2003; cf. Summa Theologiae > Third Part > Question 75), but - regardless of any observable qualities or scientific tests to the contrary -have become the "true Body of Christ and his true Blood," (CCC 1376; 1381) having been "substantially changed into the true and proper and lifegiving flesh and blood of Jesus Christ our Lord," being corporeally present whole and entire in His physical "reality;" (Mysterium Fidei, Encyclical of Pope Paul VI, 1965) "the very body which he gave up for us on the cross, the very blood which he "poured out for many for the forgiveness of sins,"(CCC 1365) with His human body and human soul, with His bodily organs and limbs and with His human mind, will and feelings. (John A. Hardon, S.J., Part I: Eucharistic Doctrine on the Real Presence)
But since her priests do not effect the actual manifest physical changes which an actual purely literal reading of the “words of consecration” at the last supper would teach, then they must engage in an extensive metaphysical explanation to justify it. For this Real Presence is not as the manifestly incarnated Christ of Scripture, whose manifest physically is so much stressed in Scripture as being opposed to a docetist or gnostic-type Christ who appears to be something he is not.
For "the Most Holy Eucharist not only looks like something it isn't (that is, bread and wine), but also tastes, smells, feels, and in all ways appears to be what it isn't." (The Holy Eucharist BY Bernard Mulcahy, O.P., p. 22)
For while bread and wine are said to have ceased to exist and Christ Himself is instead what the partakers ingest, this is "not as "sensible, visible, tangible, or extended, although it is such in heaven," but is under a "new mode of being," under the mere appearance of this non-existent bread and wine.
But only until manifest decay begins:
“The Eucharistic presence of Christ begins at the moment of the consecration and endures as long as the Eucharistic species subsist.” (CCC 1377). At which point Aquinas argued that the substance of the bread and wine (which no longer exists) cannot return, despite appearance. (Summa Theologiae, Question 77)
To inhibit this decay, Catholic instruction requires that the bread used in the Eucharistic Sacrifice must be unleavened, while hosts that are completely gluten-free are invalid matter, which thus causes problems for many Catholics with Celiac disease due to the adverse effects to the non-existent gluten.
Therefore the answer to the question to as whether the early Christians universally assumed the Catholic doctrine of the doctrine of the "Real Presence" to be true is that this is simply not what is evidenced in the light of the only wholly inspired authoritative source on what they believed. Which was neither a purely literal understanding of the "words of consecration" much less that which is justified by somewhat using Aristotelian substance theory, while the metaphorical understanding alone easily conflates with Scripture overall. See here for an extensive examination of this issue, by the grace of God, with Eucharistic theology being just one of many Catholic distinctives not seen in the inspired record of what the NT church believed.