I wrote a very simple script that did linear scaling between 36 to 70c, and it did a fantastic job of keeping my GPU at reasonable temps. It really doesn't need to be that complicated to function well.
Setting fan speed to max would also do a "fantastic job of keeping my GPU at reasonable temps."
Linear scaling means your fan is not going fast enough at high temps, and is going too fast at low temps. If your GPU is at 30C, the fan should slow down. It will be at 45C instead, which has no effect on ageing. Likewise, if your target is 45C, your fan isn't going nearly fast enough at high power.
Setting fan speed to max would also do a "fantastic job of keeping my GPU at reasonable temps."
Linear scaling means your fan is not going fast enough at high temps, and is going too fast at low temps. If your GPU is at 30C, the fan should slow down. It will be at 45C instead, which has no effect on ageing. Likewise, if your target is 45C, your fan isn't going nearly fast enough at high power.