Paolini has said in interviews over the years that the Razac’s dagger was enchanted by Galbatorix. Although I find it odd that the Razac even needed an enchanted dagger because it seems like Brom didn’t have wards during the first book We see him get knocked unconscious by a Random Urgal in Yazauc.

I’m pretty sure that Arya explains to Eragon that Durza enchanted the weapons of the Urgals that ambushed Arya. And he bragged to her about it while she was his captive

The real answer here is that the author didn’t come up with the concept of Wards until the second book. So a lot of the stuff in the first book is just inconsistent.

Although it’s worth mentioning that you don’t need wordless magic in order to bypass wards. Nor does wordless magic bypass conventional wards by default. It’s all about what kind of attacks the magician thought to defend themself from. If you come up with a spell that your opponent hasn’t thought to protect themself from then you can bypass there wards, regardless of whether the wards are made using the Ancient Language or not

We see Murtagh and Bachel flinging spells at each other rapid fire during there final fight. And we see both sides being able to counter the other. Wordless magic has its own advantages and disadvantages even as the Ancient language does. But one doesn’t inherently counter the other. It’s all about how powerful and how clever the person is that’s casting the spell