It's hard to take the statement of Zody/Hydie being Primals seriously at the moment. One, because, all Ascians are lying scumbags who want to sow disorder in order to further their own plans. Two, Solus is considered pretty sketch compared to other Ascians to boot. Three, there's a lot of strangeness about Zody/Hydie that doesn't sit right if they are simply Primals.

For instance, we've never heard of them being referenced as Primals before. Even back in the days of the Allagans, there hasn't been mentioned anything about the world itself being an Eikon (Which, I'd assume would be a more accurate term for them IF they are indeed Primal-like entities, given that while Garleans have adopted the word Eikon, an Eikon is something slightly different to a Primal)

Hydaelyn seems to exist outside of the world. She's in the Aetherial Sea. She can guide people there and exists in that space. She doesn't appear in any physical form. Unlike actual Primals whom only seem to exist when they have that particular simulacrum summoned - Which has been noted, is not the ACTUAL version of themself, hence the issue with Bahamut when Tiamat tried to summon him.

Hydaelyn and Zodiark aren't sucking up all the Aether from the world. Which you'd expect if the shards are supposedly pieces of them, that all Aether would get gobbled up, due to that being literally the most important thing to note from Primals as that's why they're so dangerous to let live and why Alexander wants to keep out of action since he doesn't want to destroy the world by nomming all the Aether. To say nothing about Hydie being in the Aetherial Sea which is, full of Aether. Yet it's all not nommed and in fact, the opposite is true and Hydie is actually weak because of spending so much effort aiding WoL's.

There doesn't appear to be any tempering going on. Normies are still going around praying to the Twelve, not going around doing the bidding of the Mother/Father crystals. In fact, it's only the ones whom possess the Echo (Which, according to the Ascians themselves, prevents tempering) that are actually involved with Zody/Hydie (Though, we're unsure if Zody is actually capable of granting the Echo himself or not, or if Ascians were given it by Hydie and then for some reason, started trying to ressurect Zody)

Even IF Hydie was a Primal and the WoL's was tempered... Then it wouldn't make sense that they would be able to go off and become Warriors of Darkness. There's no evidence of someone who's tempered by a Primal being able to get re-tempered by ANOTHER Primal. So, both us becoming WoD's in ShB as well as the WoD's we met in HW have no reasonable explaination as far as Tempering goes. Everything has suggested that Tempering is irreversible (Though, I guess we've never actually had anyone try to be re-tempered...)

So yeah... I'll reserve my judgement on the validity of Solus' statement, as is now it seems like it's designed to just be shocking if taken at face value, but with not a whole lot suggesting the accuracy of such a statement.