You won’t get your PhD without passing, so it matters.
It may be that your examiners have very few issues with your thesis, no problems to tackle, but they still have to have a good discussion with you. The PhD is for you – the thesis is part of the proof that you have hit a certain high standard. So while the thesis could be convincing, you have to be too.
You have to pass on the day, but you already have to have passed many other challenges. You have to pass, but really you have to already be able to pass to get to the viva.
The viva matters, but don’t forget the journey you’ve completed to get there.