The EO Churches cannot be said to the one catholic Church we profess in the Creed, because they are simply not one. Many of their theologians even admit that the an ecclesiology that acknowledges one universal Church necessitates the primacy, which is why they try and defend a purely Eucharistic ecclesiology. They are simply a collection of particular Churches (a particular Church being defined as a bishop and flock celebrating a common Eucharist). They separated from that one, universal Church.
A Ukrainian Orthodox person should be acutely aware of this, given the multiplicity in Ukraine itself. They constantly get into situations where EO particular church A is in communion with B, B is in communion with C, but A and C are not in communion with each other (A=B=C≠A) (e.g. the current schism between Constantinople, Moscow, and some Ukrainian Churches; ROCOR; the Moscow-Contantinople schism in 1996; the Bulgarian schism of the 19th century when most patriarchates, but not Moscow, broke communion with the Bulgarian Churches; etc., etc.). How can one universal/catholic church simultaneously have some particular churches in communion with other particular churches, while other churches are separated from each other? That’s not unity. This can only make sense if there is a plurality of Churches–the “one” of the Creed is lacking–and without this oneness, the very concept of one catholic/universal Church becomes untenable.
This was illustrated perfectly by the recent pan-Orthodox Synod (or whatever it ultimately was classified as). It barely even got off the ground because Churches were threatening to boycott (and many did) because they were fighting with other Churches over who had jurisdiction over what. Despite the EO polemics about all bishops being equal, if you look at how that synod was explicitly organized and carried out, the bishops who participated in that synod did not do so as equal bishops of one Church, but as representatives of multiple national Churches and patriarchates. What was sought was not a consensus of the bishops of one Church (or even a consensus of particular Churches), but rather a consensus of independent national Churches–which didn’t happen anyway.