I've owned both at the same time.
WR: Will go anywhere in the dirt but will wear you out on the pavement. Perfect bike if you are only on the pavement to connect to another dirt trail. Most fun dirtbike I've ever owned. Mine was an '05.
XRL: Owned two. The first I modified the carb and exhaust
and air filter and never could get it jetted correctly. The second I left stock and it ran great at 11,000 ft and -280 ft. An OK bike to ride on the road for up to 200 mile days and is also OK in the dirt. The XRL is much heavier than the WR450F, doesn't have as much power, doesn't have as good suspension.
WR: 90% dirt and 10% pavement
XRL: 50% dirt and 50% pavement
For tight technical 4x4 trails the WR is dramatically better.
For deep sand and big whoops, you can ride the WR as fast as your skills allow.
The XRL is a worthy dirt bike but you have to ride it slower than the WR because of the suspension, power and weight.
If money was no object I would own both. They are both very good bikes but they are different.
It really has to do with where you ride and what compromises you are willing to live with.
For 1st and 2nd gear trails where you never ride faster than 20 MPH, buy a WR250R.
For desert and faster riding buy a WR450F and plate it.
For 80% pavement and 20% dirt on rides of more than 500 miles, buy one an "Adventure Bike" like an R1200GS BMW or KTM 990.
All these bikes are very good and they are also very different.