You have to do it to support modern game graphics. It is something they could skip if they didn't do modern game graphics. It is a cost of modern game graphics. Doesn't matter if you disagree, this is a fact.

So if you divide it up, how much work is done to support the art and graphics of the game, and how much is done to support the gameplay, you get a much greater ratio art to game than 60/40.

By that reductionist logic anyone who writes features for UI, or cosmetic only physics (ragdolls) is supporting modern game graphics?