I hear what you're saying but the skill losses you're projecting over time seem really surprising to me.
as far as i know, this business of understanding the rate of decline only has anecdotal data. my experience also has some traumatic moments, but my rule of thumb is the player losing 25% of his TSP between 33 and, say, 41 or 42. But perception is also important: You see Sawyer as a negative -20 and remember his peak; i see that he is an exceptional player, even if 37.
But the larger point, for me, is developing a system for cycling new talent into the team. At the NBBA, i am convinced no one can waste valuable roster spots on training promising teenagers. That leaves the TL as the source of fresh blood. And within that TL, the least expensive talent are older players. If avoiding relegation is the goal (and it is for me), then older players are the most cost-efficient way to achieve that goal.