Draisaitl has the size and strength to still be able to compete without speed, though. To be effective on the ice, you need to either be fast or big/strong. If you're both slow and physically weak, it won't matter how technical you are. This is why players get worse as they age. A 45 year old player is still going to have the knowledge and "IQ" but the fact their physical abilities are so far below the younger players makes them unable to compete.
I get that it’s not the same with bigger players like Draisaitl, who is also just better, but aging also affects your IQ. Your ability to quickly process things slows down as does your endurance which means you can get mentally fatigued quicker. You also lose reaction time, dexterity, hand-eye, etc. These are things that shouldn’t be affected for Pettersson, except maybe a lack of endurance from his offseason training affecting his mental game. There’s players who aren’t fast or physically imposing but get by on smarts and skills and Pettersson isn’t a stupid or unskilled player. Without his speed he isn’t going to be a 100 point player, but he shouldn’t be a 50 point player either.