Looking at this site:
2018-19 NHL Summary | Hockey-Reference.com
They have a stat called SOS (strength of schedule)... which evaluates every team's opposition based on goals for/against and the Oilers have had the toughest schedule so far this season so it's not just our perception that the schedule has been difficult... it's reality.
That doesn't fully excuse their play so far.. because the other stat on that site is SRS which rates all the teams based on their results INCLUDING taking into account strength of schedule and the Oilers come out at 21st overall.
Honestly that's probably pretty accurate... because last season they were 21st in that SRS stat as well and can you really say the team is better this season than last? Not really. McDavid is better and the rest of the team may have actually taken a slight step back.. which keeps them basically exactly where they were last year. On pace for 82 pts right now feels about right as well... just an ever so slight improvement over last season.