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What is going on in here..............

No you are not wrong. You'll be fine, no need for a oil catch can.

 

Blowby is essentially oil vapors that get recirculated into the intake tract of the motor (this means you have oil mixed with clean air going into the combustion chamber of the motor). On naturally aspirated cars, this isn't so much of an issue since the cars are less sensitive to fuel mixture predetonation AKA knocking. On a turbocharged car like a WRX there tends to be more blowby thus diluting the overall octane of your gas leading to more knock.

Additionally, you get recirculated exhaust vapors in the intake of most modern cars for emission compliance, this means you have sooty gunk that will get put back through the motor. The catch can is supposed to filter this junk out so it doesn't go back through the motor. But in the case of a 2015+ WRX, BMW or any other DI car, there is no fuel wash on the intake side of the intake valves, so you get soot buildup on the valves. The dual DI + port injection helps to combat that by washing the valves.

I hope this helps.