It should be noted that many scholars who study the origins of Samaritanism are happy to accept the early Christian sources. My teacher Rory Boid of Monash University is quite happy to explain the name as deriving from an individual named Dositheus. After all, the names seem closely related - at least on the surface. There is one difficulty however which is difficult to explain and the same problem resurfaces in what follows in our oldest source for the sect, the 'Outlines' or 'Memoirs' (Ὑπομνήματα) of a certain Hegesippius (Ἡγήσιππος).
The question here is, even if you accept that דוסתאן and Λοσιθιανοί are related, there is only way that to explain the linguistic relationship. דוסתאן derives its origins from Λοσιθιανοί which in turn is rooted in the singular Latin Dosithianus Latinized Greek Λοσιθιανός. This Latinized Greek form appears throughout the Memoirs and is epitomized by the familiar - but unusual form - 'Christian' viz.
Christus + -ānus or from Greek Χριστιανός.
The -ian ending is Latin. There is no mistaking this. Why then does an Aramaic speaker like Hegesippus, a man who uses a Hebrew gospel, consistently construct the names of sects in a Latinized form? The argument that the existence of Χριστιανός in texts like the Acts of the Apostles 'proves' that this habit was widespread is not convincing. Rather, we must assume that it is more likely that the same hand who edited the 'final edition' of Acts translated some other terminology designating the name of the first community of Jesus believers as Χριστιανοί. Indeed Epiphanius had in his possession a Hebrew or Aramaic edition of Acts where Eeshim (אִישִׁ֔ים) stood in the place of Χριστιανοί in our text.
To this end, we should begin to suspect that an Aramaic text of the 'Memoirs' explained strange terms like Dostan (דוסתאן) in ways that could be made sensible for its readership. In other words, the translator - perhaps Irenaeus - saw the unusual ending 'an' ending in דוסתאן and read it as if it were the Latin suffix 'ian.' Indeed we shouldn't forget how important the 'Dositheans' were to the development of 'heresies.' In Hippolytus's syntagma for instance 'Dositheus' the alleged leader of the sect was listed as the head of all Christian heresies. This is usually examined in terms of its significance for understanding early Christianity - viz. that 'Dositheus' is represented as being a Samaritan precursor of Simon Magus, the man usually identified as the first heresy in Christianity.
Yet I think we should turn this around and think about this only as a linguistic precedent. The translator of the Aramaic original of the Outlines (or perhaps some other source incorporated into his final edition) was confronted by a Samaritan sect named the דוסתאן. The translator took the initiative to explain the curious form as a Latinized group name meaning 'those of Dositheus' and this 'first of the heresies' served as the justification or gave way to the idea to render all names in their Latinized Greek form (i.e. 'Christianoi,' 'Marcianoi' etc).
For it is well established that the form דוסתאן was the proper name of the sect outside of Abu'l Fath. The Samaritan writings make consistent reference to the form. Those who study Samaritanism for the most part recognize the term as deriving from Persian - i.e. دوستان which means 'friends' or 'lovers.' Stenhouse inserts this very explanation into his translation of Abu'l-Fath and the etymology is recognized by authorities as far back as Nutter.
In other words, in the same way as Masbotheos is not the real name of a sect called the 'baptizers' (Hegesippus - 'καὶ Μασβωθεος, ὅθεν Μασβωθεοι) the Dustan were not founded by a man named 'Dositheus.' Rather they were simply a group which identified themselves as 'friends' in some capacity. The incorporation of Persian terminology into Hebrew already appears in various places in the Torah and likely points to the great antiquity of the sect. Yet more significantly perhaps the use of Dustan throughout Judeo-Persian - the language of Jews living in the East - especially in their translations of the Bible is highly significant.
In other words, what I think happened historically was that the name of the sect may have been rooted in a Persian word. The Greek is just a clumsy attempt to make sense of the terminology. Some examples of what דוסתאן replaces in the Judeo-Persian texts:
Rejoice with Jerusalem and be glad for her, all you who love (אֹהֲבֶ֑יהָ) ; rejoice greatly with her, all you who mourn over her (Isaiah 66:10)
I have forsaken my house; I have abandoned my heritage; I have given the beloved ( יְדִד֥וּת ) of my soul into the hands of her enemies (Jeremiah 12:7)
And you, Pashhur, and all who live in your house will go into exile to Babylon. There you will die and be buried, you and all your friends ( אֹ֣הֲבֶ֔יךָ ) to whom you have prophesied lies.' (Jeremiah 20:6)
All your lovers (מְאַהֲבַ֣יִךְ) have forgotten you; they care nothing for you. I have struck you as an enemy would and punished you as would the cruel, because your guilt is so great and your sins so many. (Jeremiah 30:14)
And so I handed her over to her Assyrian lovers (מְאַֽהֲבֶ֑יהָ), whom she desired so much (Ezekiel 23:9)
I think this is a very significant breakthrough in terms of understanding the origin of Christianity - not merely Christianity - because it demonstrates first and foremost how much of the information about the early sectarian groups develops from misinformation and misunderstanding.