And I'm simply point out that if the air being sucked in from outside is contaminated, then the air inside will be similarly contaminated. Any meaningful analysis needs to look at the entire system. If the ECS system can't filter out contamination coming from the engine internals, then it won't be able to filter out similar contamination coming from outside the aircraft.
Look, a fume event caused by an engine oil leak is bad news for the people who are breathing the fumes. No argument. But such events are rare (especially since the most common culprit engine/aircraft are disappearing from service). Before I retired, I checked the incoming 21.3 reports at Boeing for fume events for about six months. There were a number of fume events, but only three were somehow related to the ECS system - most were galley events with the odd electrical smoke event. Of the three, one was an improper engine water wash, one was reported as an actual engine oil leak, and one was an air-cycle machine failure on a 787 (you know, the one aircraft that doesn't use engine bleed air). So fume events due to engine faults are pretty uncommon. (BTW Gnadenburg, while it certainly smells unpleasant, the stuff they use for an engine water wash is pretty benign - many use just plain water. If there is anything particularly toxic, it came from the 'dirt' that was washed off the blades, not from the cleaning solutions. If the wash is done properly the bleeds are blocked such that nothing gets into the bleed system, but sometimes mistakes are made).
What is often claimed is that 'normal' engine bleed air is a hazard - but there is little data to support that. If the infinitesimally small amounts of engine oil that finds its way into the engine bleed system from a healthy engine is a hazard, then the far higher concentrations that get sucked into the aircraft at and around the airport would constitute a hazard.