There can be no doubt that Abul-Fath is using an ancient description of the sect which was known to both Origen and Epiphanius. The Church Fathers however identify the sect leader specifically as Dositheus and the group the 'Dositheans.' The earliest known source which does this is Hegesippus's Memoirs c. 177 CE:
ἄρχεται δὲ ὁ Θεβουθις διὰ τὸ μὴ γενέσθαι αὐτὸν ἐπίσκοπον ὑποφθείρειν ἀπὸ τῶν ἑπτὰ αἱρέσεων, ὧν καὶ αὐτὸς ἦν, ἐν τῷ λαῷ, ἀφ̓ ὧν Σίμων, ὅθεν Σιμωνιανοί, καὶ Κλεόβιος, ὅθεν Κλεοβιηνοί, καὶ Δοσίθεος, ὅθεν Λοσιθιανοί, καὶ Γορθαῖος, ὅθεν Γοραθηνοί, καὶ Μασβωθεος, ὅθεν Μασβωθεοι· ἀπὸ τούτων Μενανδριανισταὶ καὶ Μαρκιανισταὶ καὶ Καρποκρατιανοὶ καὶ Οὐαλεντινιανοὶ καὶ Βασιλειδιανοὶ καὶ Σατορνιλιανοὶ ἕκαστος ἰδίως καὶ ἑτεροίως ἰδίαν δόξαν παρεισηγάγοσαν,
But Thebuthis, because he was not made bishop, began to corrupt it. He also was sprung from the seven sects among the people, like Simon, from whom came the Simonians, and Cleobius, from whom came the Cleobians, and Dositheus, from whom came the Dositheans, and Gorthaeus, from whom came the Goratheni, and Masbotheus, from whom came the Masbothaeans. From them sprang the Menandrianists, and Marcionists, and Carpocratians, and Valentinians, and Basilidians, and Saturnilians. Each introduced privately and separately his own peculiar opinion
The problem here is clearly that while 'Simon' certainly sounds like a real name - and thus 'the Simonians' represent a real sect - many of the sects here which are linked with an alleged founder are not to be so understood.
For instance, the bishop here identified as Θεβουθις is really a Greek corruption of the Hebrew word for abomination or תּוֹעֵבָה. More importantly, the Masbothaeans are clearly not derived from a man named 'Masbotheus.' The name is clearly an Aramaic term which means 'baptizers.' As such we find the starting point at least for our understanding that the phrase 'and Dositheus from whom came the Dositheans' ( καὶ Δοσίθεος, ὅθεν Λοσιθιανοί) is a misunderstanding or a false explanation of a name preserved in Aramaic which described this sect.