Car Mastery perks that are broken/insensible

Some cars have duplicates of the same perk and their combined effects don’t work or are just designed insensibly. One car has two perks for skill song multiplier: one adds 1.5 speed and the next 1.75 speed. However there was no step increase. It still increases 1.2, 1.4, 1.6…

Another car has +5% combo score and then a +15% combo score. Both unlocked youd expect +20 but it only gives +15. What is the point? Just a waste of unlock points.

Also the 10 time event finish perks dont always count the race.

Is the system buggy or just designed poorly l wonder.