Sure, just blindly looking at WAR, is not recommended.
If you take dwar out of it and just compare his offense to other first basemen, he's a below average hitter at the position. You can bump him up to average taking his durability into account which is really what WAR is doing by using "above replacement" as the base instead of average. In that respect, WAR helps him rather than hurts him.
Then you have to decide whether his defense hurts or helps his value, again compared to other first basemen which is the lowest bar for defense.
Finally, you have to consider the value of a first baseman compared to other positions. I think you have to say that the ability to play more of a skill position would increase a player's value. How much of a difference? You could choose your own positional value if you don't like the one Tango and others suggest.