In this version of Narnia, Telmarine armorers have an inordinate fondness for morions. A culture with a trace of creativity should have more than one kind of helmet. Also, the Telmarine army seems to base too much of their close order drill on the Uruk-hai field manuals 22.5 (holding your weapon with your arms extended while marching, which is really fatiguing if you are made of flesh and blood rather than CGI) and 22.6 (stamping your feet as loudly as possible on the march).
On the other hand, I wasn’t bothered by the Telmarine siege machines and their casual defiance of physics as we know them. Because, this is Narnia, and the physics are different there. This is a world where gryphons can not only get airborn, but carry human payloads.
With Narnian physics, all you need is enough laminated Dryad wood for your siege machine components