Serious question—if you were on a tight deadline, why did you choose a tech stack that you still had to learn? Leveraging existing knowledge is exactly what anyone in a rush should be doing.
Also bear in mind that I'm only covering my front-end perspective on this. I think the back-end developers involved on the project found it much easier to work with as they were already experienced with Elixir and Phoenix. For them, a tightly-coupled front and back end meant that they could change the way things worked and it was straightforward to update a few functions in Elixir and then the HEEX template, as opposed to a decoupled setup where we'd probably have been communicating using a JSON API and changes would have had more of a barrier to adopt.