There's a raging debate going on about which of these two aspects are more important towards winning Bridge( at our bridge association).
So far most say it's 70% bidding... Other than me and some reluctant voices.
You quote some guru and the reply is that as he has to sell that book which is on "this" aspect of the game so is bad mouthing the other.
If this issue has been done to death, then apologies and be kind enough to provide the link(s).
Plus... it's free!