I think you’re splitting hairs. Most authorities would say that Islam is as valid a spiritual system as Xy. They would say that the faithful of that religion are living in the favor of God.
Salvation isn’t the “bottom line” where the validity of other faith systems is concerned.
From:
Extra Ecclesiam nulla salus - Wikipedia
The
Latin phrase
extra Ecclesiam nulla salus means "outside the Church there is no salvation".
[1][2] The 1992
Catechism of the Catholic Church explained this as "all salvation comes from
Christ the Head through the Church which is His Body."
[3]
This expression comes from the writings of
Saint Cyprian of Carthage, a bishop of the
3rd century. The axiom is often used as shorthand for the
doctrine that the Church is necessary for
salvation. It is a
dogma in the
Catholic Church and the
Eastern Orthodox churches in reference to their own communions. It is also held by many historic Protestant Churches. However, Protestants, Catholics and the Orthodox each have a unique
ecclesiological understanding of what constitutes the Church. The theological basis for this doctrine is founded on the beliefs that (1)
Jesus Christ personally established
the one Church; and (2) the Church serves as the means by which the
graces won by Christ are communicated to believers.
Kallistos Ware, a Greek Orthodox bishop, has expressed this doctrine as follows:
"Extra Ecclesiam nulla salus. All the categorical strength and point of this aphorism lies in its
tautology. Outside the Church there is no salvation, because salvation is the Church" (G. Florovsky, "Sobornost: the Catholicity of the Church", in
The Church of God, p. 53). Does it therefore follow that anyone who is not visibly within the Church is necessarily damned? Of course not; still less does it follow that everyone who is visibly within the Church is necessarily saved. As Augustine wisely remarked: "How many sheep there are without, how many wolves within!" (Homilies on John, 45, 12) While there is no division between a "visible" and an "invisible Church", yet there may be members of the Church who are not visibly such, but whose membership is known to God alone. If anyone is saved, he must in some sense be a member of the Church; in what sense, we cannot always say.
[4]
The Catholic Church also teaches that the doctrine does not mean that everyone who is not visibly within the Church is necessarily damned in case of inculpable ignorance.
Some of the most pertinent Catholic expressions of this doctrine are: the profession of faith of
Pope Innocent III (1208), the profession of faith of the Fourth Lateran Council (1215), the bull
Unam sanctam of
Pope Boniface VIII (1302), and the profession of faith of the
Council of Florence (1442). The axiom "No salvation outside the Church" has been frequently repeated over the centuries in different terms by the ordinary magisterium.