That actually isn't too bad. A good synthetic that works nicely with DI engines, such as Pennzoil Platinum, would have went a long way towards preventing that. Plus a good "Italian tune-up" every once in a while.
Of course I am just guessing, but it looks like it was just around town driven and used sub-par oil (the build up is caused by the oil that gets through the valve seals to lubricate the valves coking and not being cleaned by fuel since DI injectors are not in the intake tract).
I have seen non-DI engines worse than that.
I catch-canned my Mazdaspeed, but it was built before manufacturers worked to prevent this coking with tuning to help minimize it. Of course it is still going to happen, but not anything like the early days of DI.
Use good oil, change it often, run the piss out of it every once in a while, and a good DI valve cleaning treatment every now and then won't hurt either. It's no cure-all, but it can't hurt.
2018 Machine Gray Mazda 6 Grand Touring 2.5 Turbo 35% tint, OEM splash guards, LED bulbs inside and license plate, Orange Virus Tune (coming soon), Corksport intake (coming soon), modification to area behind the grill to bring more air to the stock airbox scoop with K&N filter, Maxpider 3D floor mats, G2 silver caliper coating.