I have long felt that the material under the name Eusubius is much like that under Epiphanius, Origen and Irenaeus. That is a collection of material from various authors, which has been collected into a compendium by some middle ages editor.
In a sense this is not much different than the Pauline letters of the New testament, where theories, on often very sound grounds, argue that several of the books are in fact made up of fragments sometimes of other letters (e.g., most of Galatians 3-6, 2 Corinthians 8-9, Romans 16, etc) or passages made up by the collector of the fragments who put them into letter form, or by the editor who bound them into a collection, or the redactor who Catholicized them more or less into the form we have now.
From that perspective, the concept of "forger" is perhaps incorrect, as this goes back to the assumption of single authorship and these works being held so sacrosanct as to be untouchable Canon. There is however zero evidence that the Church Father writings were ever considered sacrosanct, and they were copied, rewritten, cobbled together for arguments like fragments we see in text books today.
While not challenging in the least the existence and relationship of the material under the name Eusubius having problematic relationships with other materials, nor that at some stage the compendium of material obtained made up speeches (what ancient writing, including the NT and also the OT is not full of made up dialogue?) and made up sources (or at least "adjusted" to fit the argument at hand), I would suggest we change our perspective to examine the content of the church father writings as snowballs. The more important the author --few would argue that Eusubius is the most important for church lore ("history") to this day-- the more likely it would attract improvements and additions.
None of this is to say that, like the Pauline collection, there are layers of earlier material that may even date from the ascribed author's reputed era. But the presence of snippets from earlier days does in no way mean all the material is early, or that the work is a unity, expect from the later editorial hand that we measure as the author (e.g. the Lukan redactor of Luke-Acts leaves a distinct hand, but we are well aware of an earlier form of Luke and that both Luke and Acts are composed from many source documents). So some of Eusubius may in fact be from his hand.
Anyway I very much welcome this rising awareness that the Church Father writings are problematic, the true authorship unknown, and the pseudo autobiographical material suspect, more legend than fact, and even the dating of the material questionable (since it's often based on the dubious legendary pseudo biographical commentary). It is a healthy development.
“’That was excellently observed’, say I, when I read a passage in an author, where his opinion agrees with mine. When we differ, there I pronounce him to be mistaken.” - Jonathan Swift