I checked just now, and Jagger's knighthood was, logically enough, for "service to popular music." I seem to recall liking some of his songs 'way back when. I'm not much into music in general, so I haven't kept up, but apparently he's still at it (and well regarded) in his eighties.
Jeremy Brett is mostly known for just two roles, Freddy Eynsford-Hill in the movie My Fair Lady and of course Sherlock Holmes. The latter, especially, is very high-quality stuff, but due to his poor health and his death at age 61, there was precious little of it.
Not sure how the two could be compared. (Though I won't exactly argue with you. )
We are NOT one of those stuffy forums that will scold you for posting in an "old" thread. In fact, as long as your post is polite, relevant, and all that usual stuff, we actually enjoy new input!