The issue with that, of course, is the fact that in most test matches, over two innings from a batting side, 6 wickets or so DO tend to go down for less than 22 anyways... When you consider tailenders and such...
Also, the whole thing about there are less bowlers than batsman in any side and so they are more valuable coz they contribute more comes down to opportunity as well.. If you got 5 bowlers in your side who bowl regularly and assuming an innings lasts 100 overs, a bowler gets 20% of share to make his contribution... With a batsman, it is not that simple to work out something like this. So while the pure stats make it look great with Murali averaging 6 wickets per match at about 22 runs and Sachin averaging 55 with the bat, the reality is that since Murali's 6 wickets include tailenders and stuff who generally do get out for low scores, it is not as if he is easily more valuable than Sachin.
Of course, I do rate Murali > Sachin and even though I used their names here, I am more generally just making a point about batsmen Vs bowlers...