I'm not sure. I like having him involved in pivotal events, because it brings them to life for all of us (inasmuch as I can write it that way). They do require more research, though. I think that it becomes tougher, as you noted, when he becomes more senior, but rest assured I'll figure a way around things.
There are some lines I can't cross, though. It's been explained to me that Granger can't have sex with truly heroic figures of the era (the most obvious being Nelson). I guess that would extend to Wellington, too, although it would have been good for him, because I always felt like he had a stick up his ass.
I think that you're right about this one.