I'm saying two things:
Getting fouled in a more dangerous attacking position is more valuable than getting fouled in your own half for example.
And with that as a basis someone whose job is to attack getting fouled more is probably more valuable overall and makes that person better at doing their job specifically than someone who is tasked with doing the things midfielders do.
In your example of the goal saving tackle the action that matters is the tackle. Whether the guy is fouled, passes it to a teammate, hoofs it out of bounds or whatever else they can do the part that matters is that they stopped the attack with the tackle. For an attacker that dynamic changes more because the act of drawing a foul can directly lead to shots at goal which is typically the only way to score a goal and win the game. The defender doesn't prevent the other teams shot by being fouled he prevents it by making the tackle. It isn't a direct thing.
The whole point being rating a defender because they are good at drawing fouls makes zero sense and is more of a novelty than an indication that they player is any good at playing defender/defensive midfield.
Anyway on Zaha he drew 7 penalties last season and if you count that as directly creating a chance or getting an assist when it is scored he starts to move up the list of creative players in the league pretty quickly. Not many better chances than a penalty.