I have both bikes. While the WR will eventually do everything the Tenere will, it's nowhere near as relaxed over long distance, particularly on any road.
However, the WR is a very capable trail bike, reputed to be bulletproof. They almost are. I have about 500hrs/7500km on mine. Both fork seals were/are a problem, the camchain tensioner is, erm, erratic (I have a manual one to fit soon). It also has a tiny fuel tank (7.8L), which is pathetic imo. And fuel pumps can be a problem in hot weather.
The WR is easy to maintain and is a far better off-road bike than the Tenere if things get tough.
There are people here in Australia and other countries who have done great long-distance travelling on 250Rs. For example, I'd far rather ride my WR across the deserts than my Tenere, but the Tenere would still be pretty good and much better on the open roads.
Your choice, as usual. Just don't expect the WR to be something it isn't.