Witcher's primary weapon is a sword. Magic, oils - they are always auxiliary.
I get so tired of people ranting this. I've played and finished Witcher 1 and 2 on the highest difficulty, with pure sign builds focusing on igni thank you very much.
It worked excellent, more than excellent. So don't tell me what witchers are supposed to be and no be. This third game - Witcher 3 - is the first game that actively discourages a sign build and which have bosses that are 100% immune to all signs. This was NOT the case with the previous two games.
In my mind if you give the player the option of doing a sign build it should be possible to complete the game like that, why have the option to even do a sign build in witcher 3 if the game isn't made to be played like that? It's just bad game design pure and simple. If you want everyone to just use swords there is little point in offering anything else. Like I said, bad and unfocused game design.
Good game design is giving the player freedom of choice. Look at skyrim, you can be a really powerful mage, a dual-wielding warrior in heavy armor, a really powerful archer in light armor, a sword and shield guy etc etc. AND THEY ARE ALL VIABLE OPTIONS. They all work excellent even on the highest difficulty.
Making a game that gives us the option of going for "other things" than swords, yet makes those things useless, is bad game design. Pure and simple.