So my first question is how can either the master species or their domesticated animals be highly skilled at engineering and construction without writing? What would the impact of no writing be on the civilisation? It would literally (no pun intended) limit the advancement capability of that civilisation.
Writing is one of the advances that has allowed humans to advance so quickly. Without it, the ability to transfer information between minds is greatly reduced. The novice or trainee can only learn while around their master, and only from their master. They have to listen and watch intently, and the master also has to remember what he or she has told the novice, and what hasn't been communicated yet. Also, the novice has to remember it all. Bottom line is that even if the master has come up with a new advance, it doesn't mean that the novice has the same skill to understand that advance, meaning that there's a high probability that the advance in understanding will be lost.
Writing changes that. Writing is an efficient way of recording information to share with many novices, all through time. You can add to it as you remember new things, and the novices can always refer back if they forget something you've said. Most importantly, because you've written it down, the novice in his time doesn't just re-write what he's learned from you, he writes down the stuff that's new to the practice.
Mathematics for example is the cornerstone of engineering. It's also a cumulative subject. Mathematicians have been building on their knowledge for millennia and it's important to note that while every senior secondary student today who does maths is taught calculus for example, it didn't exist 500 years ago. Leibniz and Newton (depending on who you believe) created it in the 1600s and Principia Mathematica in particular became a treatise for cutting edge mathematics that we now largely take for granted in our lives. The understanding of math at this level (and the perfect transmission of this maths into so many new minds) simply isn't possible without writing.
The reason why the Information Revolution (as our modern times will be known as in history) is so important is because we're dealing with Gutenberg Mark II; where the printing press revolutionised the ability to disseminate written knowledge and spread it among a wider population, the internet is taking that to another level again. It is that very proliferation of knowledge that is driving the proliferation and advancement of key technologies at such a rapid rate. None of it would be possible without the ability to read and write, because before YouTube you have to be able to transmit simple text because of the early bandwidth requirements. Even if that wasn't the case, I defy anyone to tell me that they can truly understand deep scientific concepts through video discussion alone; text is still a crucial element to learning and will continue to be for a long time, if not forever.
Even if that isn't the case, the ability to record an individual speaking about a topic is just a more advanced form of writing in any event. It's still recording knowledge for easy transmission, just in a far less efficient way.
So without writing, your sophisticated building capability doesn't exist. The only thing you can rely on is the memory of the individuals within your species, and their ability to articulately and completely share all their knowledge verbally with others of their species.
Good luck with that.
Seriously though, writing is the cornerstone of civilisation because it's a low energy, highly effective manner for capturing information and spreading it to others so they can use it and build upon it in their turn. Without that capability you need another way of doing that (like telepathy) which allows everyone the ability to know what you know about a specific topic, otherwise you'll lose information with every generation, like a leaky long range pipe. Some of what you need to know will eventually get there, but what will you lose along the way?
To address edits in question:
Sure, it can be argued that writing was necessary to us as a species because of otherwise limited communication abilities and less than perfect memories. With that in mind, a more perfect species capable of disseminating and retaining information more efficiently than a human mind might have less requirement for writing.
Even for such a species however, writing would still make things easier. Albert Einstein was once asked how many inches were in a yard, and his answer was 'I don't know. If I ever do need to know, I'll look it up in a book. Why clutter my mind with stuff I don't need to know when I can use my mind to come up with new ideas?' (quotes probably not required here, this is from an anecdote so I can't verify the accuracy of the words, only the intent)
The point being, that even since Gutenberg human memories have become less adept, but our reasoning skills and analytical capabilities have significantly improved. While this also ties in with the ideas of specialisation in the OP edits, writing is a low energy way of storing data that allows anyone to access it if they're curious. So even with perfect memories, it's a great way to preserve knowledge from (say) natural disasters, plagues, or some other form of destruction that could remove minds with key knowledge from the population. If nothing else, it's a backup solution.