It is as you say there are polar opposites on experience, whilst I have not owned many Subarus, in comparison to some, I have had x2 different experiences. First owned a standard STI - no issues what so ever, was maintained slightly ahead of the manual with more regular oil changes and it never missed a beat, used in all weathers but cleaned regularly and had no rust when sold. Next was an RX so NA engine had for some time used as a daily in all weathers, maintained with more regular oil changes and cleaned regularly - no issues and now with the inlaws still going strong.
Reading about engine failures etc For my next STI I went for a specialist 'built' motor to avoid the potential issues with ringland failure - within 1000 miles of my ownership I caught a gasket failure before it had chance to do any further damage - going through the car I found a lot more issues due to rubbish / shoddy workmanship.
Another STI on the drive, higher mileage engine had rebuilt using uprated gasket and bolts but standard internals, so far so good - some issues with rust on this one but it is being managed.
The outback owners would not necessarily be thrashing the living daylights out of their cars but an owner may not be as diligent on the maintenance schedule. Look for an example with a history and if see if you can get it on a ramp to check the underside (Beware of underseal it can be there to hide as well as protect)