GT Life is broken because they intertwined it with GT online: the intended method for reaching level 40, as opposed to grinding. For some reason PD is convinced that once someone completes GT life they will stop playing the game. Some might, but most wouldn't. They are intertwined in this way: they spaced out the endurance events with a 16 level spread instead of a 5 level spread like for ALL the other series (Beginner to Extreme). By making Nurburgriing 40 instead of 35 or 36, they essentially force everyone to complete the online portions of both A-spec and B-spec (1.06) or grind A-spec and B-spec to limits beyond belief. So essentially GT life is designed to be the very last thing you finish in the game if you ever do. For me this is kind of cruel for those with OCD (most gamers) because we sit here having completed 99% of the game (though really only a small portion of it) and it essentially required twice the amount of time it took to get the 99% just to get that last 1%. Right now all I have left to do in GT life officially is Nurburgring in both A-spec and B-spec. I would love to finish the last golds in each of these and then focus entirely on the online components, time trials, drifting, etc. PD is afraid that if I were to finish the A-spec and B-spec I would lose all interest in the rest of their game (and those who defend the grinding think the same thing): i.e. they think that once GT life is 100% done there is nothing of value left to play; there must always be a carrot slightly out of reach. So essentially PD and the defenders subconsciously think that the rest of the game is not that good, while those who want the levels gone, grind gone, or make the lvl 40 race a lvl 35 or 36 race actually see more value in the rest of the game than PD and the defenders do. It's a difficult concept to grasp but it's true.
It wouldn't hurt anyone to be able to complete the A-spec and B-spec Endurance series well before reaching level 40. In a well thought out game levels 35 through 40 would have been a measure of how much you played online against others or the bobs of others. But PD felt that if the single-player game were completed before the multiplayer one, the multiplayer one would be avoided or forgotten, and thus future DLC wouldn't be purchased. It's sad when developers and their butt-kissers feel the need to artificially force longevity instead of letting the game simply be what it is.
Sorry the math in my head can't ever get over the 240 hours it takes to get from B-spec lvl 36 to 40 (so I can't finish the last 1% of the part of the game I don't enjoy: there is a great attraction to the idea of never playing B-spec again, but that 1% just sits there mocking me! All because Kaz wants me to play 100s of hours of GT anywhere before I can officially call B-spec quits).
More on topic: the CR values for the endurance races were set for races ranging from levels 29 to 34, but then some nut-head spread out those races to level 40, without adjusting the CR or XP values after they did so. [They did this to fill in for the uncompleted online A-spec and B-spec.] It was the intertwining of two completely separate motives that should never have influenced one another that caused the issues.