Originality =/= individuality
Yes, it's a design. Your Veloci might also be a design. In this game, the primary difference between a design and a revision is whether or not you have to prototype it.
I reiterate: Our creatures appear to already make use of "equipment", and the Thevryn should thus be able to offload some of the costs of our most basic unit. Instant usability.
Also, the Veloci have a bunch of weird intentional failures ingrained in them, which is generally not a good plan in Arms Races, unless you want to get Very Hard for having extra "Features" and then having the bugs be "oh by the way those flaws you put in there? Yeah, they're screwing you over now".
Yes they have their purposes and that is of the creation of equipment, if we had the respective equipment to carry, they would be a support creation that incentivizes us to make equipment as it would provide a reduction of expenses in fielding those equipment. Case in point they would be a support role, and have the intention of being a thing we can specialize further upon.
The intentional weaknesses in a creature should not add difficulty to a design, that is honestly absurd, the entire point of those things is to make it easier to create or help the GM with thinking of a weakness to the design if its deployed, while also adding thematic description to the design. If anything the extra “features”, as you referred them, all provide a role for the unit and that is of increasing their combat performance, and the weaknesses is of compensating for it. However I can see of making the creature simpler just for it easier to be understood and created , but the Theryn don’t seem that simple to me.
I mean if it utilizes thing we have knowledge for, and improved upon it for our own creature, unless its really difficult with knowledge to make something muscular and strong. The Theryn utilizing of light magic to create anything, would surely increase the difficulty as we have, because they lack basis in what they have is why I’m not discouraged to choose it or recommend it