Value to a normal Test side to play other normal Test sides is actual, real value of what he actually contributed in his career. Value to some mythical ATG XI we've made up in our minds is fake nonsense that exists in our nerdy brains for an imaginary match that will never happen. It is not real world value.
What the **** in any of this is real world stuff.
In terms of what really happened, I think Marshall was better and meant more to his team than near anyone in history. He is in my opinion the greatest bowler who's ever played and was the one indispensable player and the key player that made the west indies of the '80's the greatest ever. That counts for something for me, it doesn't have to for you. Similarly for McGrath, without him, even with the rest, they aren't the one of the two greatest teams ever. Period.
Marshall succeeded in every condition vs every team and had unparalleled ability and adaptability to do so. These things count, we never played minnows to boost away or overall numbers. When everyone was on the decline or retiring, he kept us at the top and when he missed games, we lost.
That's why for me he's no. 3, but jump on one statement to make a sanctimonious one when all we do is project and play make believe.
He was amazing home and away, he dominated the SC like no one else, he was never a liability and the key to a dynasty who scared the **** out of everyone who faced him and had every skill in his toolbox, from swing, express pace, and uncomfortable bounce that caused batsman to fear not only their wicket but safety.
No other bowler in the history of the game both combined his resume and skill set.
Are those enough reasons?