If we follow St John Chrysostom then the terminology of justification by faith alone is perfectly acceptable:
The terminology of faith alone is acceptable in an Orthodox context, particularly with a baptismal theme. St. Maximus says this:
"The manner of birth from God within us is two-fold: the one bestows the grace of adoption, which is entirely present in potency in those who are born of God; the other introduces, wholly by active exertion, that grace which deliberately reorients the entire free choice of the one being born of God toward the God who gives birth. The first bears the grace, present in potency, through faith alone; but the second, beyond faith, also engenders in the knower the sublimely divine likeness of the One known, that likeness being effected precisely through knowledge."
There are similar quotes from St. Ambrose on the matter. At baptism, in a sense, we are justified by faith alone because baptism is what regenerates us and makes us capable of virtue (we become a new creation). We have nothing to offer but faith, and after baptism makes us born again, it gives us potential to be transformed as a son of God and heir of righteousness.
After that, our experience of justification in Christ's death (therefore we were buried with Him through baptism into death..) grows more into the likeness of Christ (just as Christ was raised from the dead by the glory of the Father, even so we also should walk in newness of life.) So justification does not entail sola fide in that our justification is a relational and ontological communion with God as a son which necessarily includes the virtues given to us by grace and not only faith.
While sola fide here does have a role in explaining our baptism, it doesn't really pertain to the reformation explanation of it with double imputation and faith as the "empty hand" of seizing the merit of Christ to be externally applied. Thus we cannot equivocate faith alone in the fathers vis a vis the reformers without committing the word concept fallacy.
Pastorally speaking, we ought not to use faith alone to describe our justification outside the baptismal scope. Rather, we ought to talk about the indwelling of Christ in our hearts which raises us up to new life by the Spirit by faith, hope and love given sacramentally. This is by faith, but not faith alone because we cannot maintain our baptismal garment without love and humility accompanying that faith. We should not tell the despairing they can be justified by faith alone despite their sins, since the term faith alone in this context would be assuming how it would be used in the reformation debates. It would endanger the despairing to assume that belief in Christ is all that is needed to be forgiven.
As to St. John Cassain, I would not agree with any insinuation that he was a semi-pelegian. He affirms that everything we have, including faith, is a gift from God and that God works all things in us so that we might co-work with Him. This is the opposite of semi pelegianism (which the central tenant is that faith is within our natural ability and not given by grace). And I don't think preaching the primacy of grace justifies the label of "semi-Calvinist" without assuming all the baggage of the reformation either.