Right now the alien data slate is kind of pointless, given how some of the reasearch topics you can obtain from it are also needed to decrypt it, and the random nature of unlocked topics (through the slate, as well as through interrogations). As far as I can tell, part of this is due to how alien vocabulary is unlocked - which itself requires 'advanced' topics, but doesn't unlock any new interrogation topics, despite the flavour text. It's also kind of strange that we need to research the vocabulary on top of alien language and alien codes.
This isn't a full revision, but more something i came up while looking through the research tree, taking into account what vocabulary is supposed to do (unlock advanced intierrogations) and how the slate&encryption ties into this.
My suggestion would be to tie alien vocabulary not to any advanced topics, but to interrogation of different alien ranks themselves - alien vocabulary unlocks once you have interrogated all of the alien ranks (maybe sans commander), and unlocks advanced topics that can be gained during interrogation.
Make the alien data / encryption researchable without alien vocabulary, but make it take a lot more time. As OXCE allows us to disable/hide research&manufacturing options, disable those options once alien vocabulary is unlocked and instead unlock an 'alternative' decrypt option that takes less time. That way players aren't potentially locked out of acquiring said research until they have unlocked a 'random' interrogation topic.