Unless you were bowling at, say, Jack Hobbs, or Victor Trumper (whose test average was just shy of 40, and FC average 44.5 with over 40 centuries). There were great batsmen around then too.
If the mark of a great batsman is to average 39, then what does that say about the contemporary conditions they were playing in and its knock on effect on bowling averages (which are generally incredibly low)? An Average of 39 would barely have you getting cricket in most good test teams nowadays, and I would like to see Dale Steyn's average had the best batsman of his era been so inclined.
Of course it's no more than a thought exercise to compare batsmen across eras, but doing it by stats is misleading as they obviously don't tell the whole story, as you point out. All you can really go on is how they performed against the best of their era, and the opinions of those who saw them play and played against them.
Memory can be misleading, because as time goes on, individual memories are often replaced by blanket emotional states that filter negative emotions out naturally. When we are talking about people who saw these guys then, its is also very likely that these opinions are not based on true memories, but of vague nostalgia that is biased and ignores all the factors.
A good indicator of this is the wilful ignorance of attributing certain negative factors to some eras, but not to others. Dale Steyn could never be the greatest because the discussion will always focus on actual memory, of mitigating circumstances that are fighting against a biased emotional state. I think the mention of Sidney Barnes in the opposite is a good example.... while the argument for modern batsman is "helmets, covered pitches, flat decks, etc", in an era where someone took100 wickets at an average of 10, there is never a cross over of what conditions existed then. It cant be ignored, but its not acknowledged.... cricket then was proper seems to be the opinion, not played on pitches that would probably be resulting in called off games or pitch inspector issues now. I think most bowlers would do much better in that era, and if you were to attribute some kind of mathematic formula to assess runs to wicket average across the board, you might find that Barnes ends up with a factored average that is no better than a lot of players. And lets be straight, no one on this board seen the guy play test cricket, I refuse to acknowledge that anyone can have any basis for mentioning him on anything other than paper stats without further comparative or indepth analysis. Maybe in 100 years time we might be stumbling on names like Vinod Kambli and supplanting a fake legacy for him?
don't rate Ali as the best boxer ever but your argument is right, as most say Sugar Ray Robinson.