Henman's consistency shows he was a much better all around player than he gets credit for here. The last three years of his career were marred by back injuries which is why he retired.
One could make the same argument that Sampras wouldn't have been as dominant with the likes of Djokovic and Murray around now who return so well. Returns overall have gotten so much better that big serves alone don't win majors anymore. Plus the surfaces, as was pointed out, are slower now and Sampras was a beast on the fast stuff.
It doesn't make much sense to have these discussions since the game is different now than even a few years ago. We should just enjoy Henman for what he did and lament that there isn't much of his game on offer anymore.