You're one of the few people left here that I would try to have a legit basketball discussion with. You understand that I'm not saying, "He's done." But I would hate to see him finish his career the way Hakeem did. So:
You don't think he looks like nearly the player he was at the end of last season, do you? Assuming you agree that he isn't, what would another year worth of similar fall-off look like? He would still be better than most of what passes for bigs in the league, but I don't think he'd be Timmy anymore. Do you see it differently?
Here's a few things your examples left out:
His Points/100 Possessions tied the lowest of his career last year, at 24.6. This season, his Points/100 has fallen to 17.4. That's a HUGE drop.
His FTA/100 Possessions was 7.1 last season. This season it has fallen to 4.2 - also a HUGE drop. FTA/100 is one measure of how dominant a big is, because he's forcing defenders to foul him. Tim isn't doing that nearly as much this season. It's much less than any other point in his career.
I'm surprised that his rebounding numbers (per-36 or per-100 possessions) don't look that much worse than last year. It feels like he isn't bringing them down the way he used to. But, he is down to below 25 minutes per game. I don't think he could keep it up for much more minutes per game, without those Per- numbers starting to suffer. I know you know that Per-36 can get really misleading with players getting short minutes. He still has strong nights, but in more than 1/3 of his games this season, he's had 5 or fewer rebounds - and in at least half of those (more I think) he's put in 20 minutes or more.
Like I said at the beginning, I would hate to see him end his career like Hakeem. He doesn't have to be "done" for it to be time for him to step down. While he's still Tim Duncan.