But he doesn't go the line a lot. He only attempts 4 free throws a game. In comparison with his field goal attempts, it's a higher ratio, but that doesn't really mean anything in this particular instance. He doesn't get fouled more frequently, he doesn't draw more defenders, he doesn't take more contested shots. That's a false conclusion.
The point is that he attempts a lot of free throws per shot attempt, relative to what Bird did. The whole entire point of a shooting efficiency metric like TS% is measure scoring in terms of possessions used. Obviously a team wants to maximize its points scored (and simultaneously minimize points allowed). As such, how many possessions a team gets is important, and how many points they score per possession is important. And once you shoot the ball, it either goes in (points, other team gets possession) or doesn't (no points, free rebound), and then it's time for the next possession. But every possession has to end - it ends with a shot or a turnover. Obviously, every team would prefer their possessions end in shots, and that those shots translate into points as often as possible. TS% is one step towards determining how effective a player is in scoring when he "chooses" to end a possession (by shooting).
There are a lot of things that translate into more points: creating extra possessions (rebounds, steals, forced TOs), shooting efficiently oneself, increasing the efficiency of other teammates (passing, setting picks, calling out double teams, etc.) - the last one being difficult to impossible to find in a box score.
The elephant in the room regarding the Bird/Miller question is that Bird used a lot more possessions than Miller. Maybe your objections come from the idea that had Bird been more selective, he might have been more efficient, and were Miller to shoot a lot more, he might be less efficient. You haven't expressed that specifically, so I'm not sure. But we don't know that for sure. That can only be tested by trying it - one possible approach would be encouraging players with higher TS% to shoot more often, and encouraging players with low TS% to be more selective, and trying to find an ideal balance point for the team as a whole. May not work, but it's an interesting idea.
Anyway, I don't want to sound like I'm proselytizing for TS%, as I've pointed out that it's by no means a be-all end-all stat. It's just that I don't want you to miss out on what it does tell us by focusing on what it doesn't do. (Oh, poop. I think I stole that from Jerry Reynolds!)
Which brings something else up that bothers me about this metric. You put the ball in the hands of the best free throw shooter at the end of the game when you have the lead, which increases his free throw attempts. But that doesn't take into consideration the fact that he's now shooting free throws that he didn't earn. He's not driving to the rim and getting fouled; he's getting put on the line purposely. Same basic concept with technical foul shots. These are shots that would potentially increase a player's scoring efficiency, using this metric, but really don't have anything to do with how efficient that player is with the ball in his hands.
That is a possible quibble. However, the question of how much that boosts a players TS% is interesting to think about. My understanding of the 0.44 coefficient in TS% is that it attempts to account for not only FGAs when a player is fouled shooting but also for "possessions" when a player is fouled not shooting. It's a leaguewide, long-term average, though, so star players at the end of games will probably get more than their share. (Kevin Martin, on the other hand, has spent more time
losing games than winning them, so he probably wouldn't see a boost!

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