Don’t worry about whether or not your viva will be easy or hard. Who knows what you’ll feel like on the day, in the moment?
Prepare for a challenge. Two people have read your thesis and are ready to ask you all about it. This isn’t trivial, an elevator conversation or dinner party chit-chat. It’s there to explore what you’ve done, what you could have done and what all that means.
On the day you could find this easy or hard, but it will still be a challenge.
It’s still a challenge even if you are necessarily talented.