Hythlodaeus is not a simple new recruit to the Bureau of the Architect. He is literally the chief of the Bureau of the Architect. If the bureau has no on-boarding process for the new head of the entire department, and there is no way to easily look up past records, then the bureau is a terribly-organized place that has even more unfortunate implications for the systems the Amaurotines have put into place to play god for the planet.
I'm actually being generous to Hythlodaeus here, in that I'm attributing his ignorance of Elpis flowers due to systemic issues, rather than because Hythlodaeus is a bad leader. If the only records anyone can conceivably find about the people who know about Elpis flowers and dynamis are buried deep within the Bureau of the Architect records, that Hythlodaeus never even considered looking through, then they might as well not be there at all.
Emet-Selch sounded very affronted that not only did he know nothing about dynamis, but nobody told him about it. If this is supposed to be Emet-Selch being rational, then that means he should have been told about it, either as a general member of the Convocation or in his capacity as Emet-Selch. And since he hasn't been told, that means there is nobody capable of telling him up until Hermes.Through the course of this questline we also learn that the Convocation members are all specialists in different fields, so it's no surprise that an Emet-selch specialist doesn't know about a mysterious energy that almost no one has the means or desire to manipulate. Though it is a narrative surprise because he's a big deal to us, but it's ultimately an emotional conflation.
If this is supposed to be Emet-Selch being irrational, well, that answers the question in the OP as well, since this is not a person I would be willing to join, lest his petty grumpiness lead to even more dangerous situations.
I'd like to mention that this is the same Elpis where the head of the facility created a familiar utilizing a little-known and heretofore non-useful aspect of the universe, made several copies of that familiar and networked them together, then sent those copies out into the universe, and told nobody about it until we confronted him after we managed to find a witness. There are no records about Meteion; Hermes declined to submit the concept to the Bureau of the Architect because Meteion is allegedly "still in testing" (which is fine), while also sending Meteia into the greater universe (which is not fine). This contravenes the stated rules of Elpis, and yet nobody really cared about Hermes doing this stuff until it all went pear-shaped.As for there being no way to contact the others who know about Dynamis... it's an idea that has no strength to stand under scrutiny. Elpis is a facility with rules and records. The Flower was created there, recorded there, and researched there. The names of the researchers would be in their records. The data on the flower would also be in their records.
Well, not precisely the stated Rules As Written, which limits the scope of new creations regarding Etheirys. But I feel that it's certainly contravening Rules As Intended, since if a creation has not gone through enough testing to be let loose onto Etheirys, it should follow that it has also not gone through enough testing to be let loose onto the universe in which Etheirys resides.
The statement that Ancient Amaurotine society has enough rules and records that being able to find obscure former researchers or their recorded notes is possible, much less simple, is the one that does not stand under scrutiny, if taken in context with what we're also shown in the course of the narrative. Clearly to the Amaurotines, the rules are enforced through decorum, and if someone were to break the rules, they'd just get a disapproving glance and snide comment at most. This does not strike me as a system that would be conscientious enough to have meticulous and easily accessible records.