Do you think it affects the captaincy of a team when a bowler / batsman is captain?
Yeah sure. A batsman captain can read the psychology of batsmen in better way and similarly a bowler captain can read the bowlers in better way. So there is trade off !
In my opinion a good allrounder would be best choice. We have some very good examples in form of steve waugh, Imran Khan and Kapil Dev.
Being one or the other may help in some scenarios, but for captain material the most important prerequisite is a good understanding of the game and ability to react to it. Also, a captain shouldn't let the captaincy and their own role (batsman, bowler or keeper) interfere with one another.
I think in crunch situations keepers have an excellent view of proceedings at the crease and provide valuable input if not at the helm themselves.
Overall though, I would say batsman have proven to have the edge when ot comes to captaincy.
And the best example of a good all rounder cricket in the current cricket is
Wasim Akram 
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