None of our SM cars are really competitive or fully prepared as is shown every time a real SM car shows up form Sac.

Same is true for STX, so don't count on that being a great class either without the rest of the prep work.
And there has been an unofficial "SM-B" or "SM-Tier 2" for years that WRXs all compete in. and sometimes get crushed by the elusive black RS...
Run N if you are eligible, or play with everyone else in BSP or SM. The alternative is to swap the flywheel back to stock, but the WRX isn't really competitive in stock either.
Just have fun!!!! And try and get better...