I can sort of understand why GTS has an XP/level system. My hypothesis is that PD thought having that system would be a way to add another "thing to do" between updates. It also gives incentive to race clean both online and in GT League, and in the former, an incentive to try winning with underpowered cars, in some events. But hopefully in the next title, they'll do away with the exp/level system. The exp/level game mechanic is meant to simplify the otherwise abstract concept of gaining experience, especially in RPGs like Dragon Quest, Pokemon, SMT, and Final Fantasy. I'm almost tempted to say that exp/level systems in general are abused in game design, and that there are far less places where they belong than where they actually are appearing. (I'd say the same of GTS' in-game achievements, where I understand why they exist, but I don't think they'd be good content to see in the next title.)
For GTS, I would say the Driver Rating system is a superior way to have a metric on experience & skill. Not that I'm saying it's the best way to simply the concept of experience that I could possibly comprehend, but I think it's better than an actual exp/level mechanic that's right beside it in GTS. I would also argue that having your profile show where you've obtained 100% in various campaign sections (I think GT5 did this) would also be a good way to show how experienced/skilled you are. I also really like Kudos' "Speed Score," where they offer a metric that's based on how close you come, percentage-wise, to the best qualifying time for a given event. I really do like seeing the region gaps for my times, as well as where my time ranks within that region.
It'd also be nice if we could see the "narrower levels" of where our times may rank, like by nation or state, but that's another matter.
I also think the easier license tests of the PS3 era and onwards should be combined with the mandatory need for licenses in the PS2 era, as I think the latter concept was especially marred by the difficulty, whereas the PS3/PS4-era license tests are comparatively much easier. (Not too easy insofar you don't need to think, but just hard enough to force you into gaining further game literacy.) If the mandatory need for licenses from the PS2 era were combined with the relatively easier tests from the PS3/PS4 era, maybe there could be a further sense of progression by having a vastly reinterpreted version of GT5's level requirements for car ownership, in that licenses could permit players to buy (and thus, race) more advanced vehicles. Here were my ideas for what licenses would permit the use of which cars/classes:
-National C - N-series cars up to N200, and the lowest-level Gr.X cars like the BMW i3, and GT Kart 125.
-National B - N-series up to N400.
-National A - Gr.4, N-series cars up to N600, as well as other Gr.X cars like the Red Bull X2014 Jr., the Tesla Model S, the Honda 2&4, and the Toyota FT-1 Concept.
-International B - Gr.3, remaining N-series cars, the Subaru Time Attack WRX, the Gr.X-spec R.S.01, and the track-day Gr.X cars like the P1 GTR and Zonda R.
-International A - Gr.2, and the various vintage race cars within Gr.X.
-Super - Gr.1, all Gr.X-spec VGTs, and the highest-powered Gr.X cars such as the F1500T-A and all other Red Bull cars.
-Rally - Gr.B (Obviously.)
EDIT: Re-arranged some stuff.
