Clearly a lot of people didn't watch Karlsson outside of highlights, because when he was asked to play conservative and focusing on shutting down the opposition defensively, he was always elite at doing it. The problem was he was always asked to carry the team offensively, which meant taking a lot of risks, and risks don't always work out. There's a reason everyone refers to 2016-17 as his peak season, even though his scoring was actually a bit lower from previous seasons, and that's because the new coach actually implemented a proper system, and Karlsson didn't have to do literally everything himself.
If you actually watched both Makar and Karlsson play, you will notice that the two have a different approach to the game, and different responsibilities as players. Because Colorado is a lot deeper than any of the Ottawa teams that Karlsson played on, Makar tends to "pick his spots". He's not going balls-to-the-walls, driving the play, controlling the pace of the game every time he's out on the ice, which is how Karlsson played during his prime. Makar holds onto the puck a whole lot less than Karlsson did, and his typical shift is him passing the puck off to a teammate to rush up the ice, waiting for the right moment for space to open up in the offensive zone, and then he'll use his speed to get open and create a dangerous scoring chance. That's different than what Karlsson's typical shift looked like, which was try to breakup the play in the defensive zone, skate the puck out of danger, skate the puck up the ice, circle around in the offensive zone with the puck until a teammate gets open. Karlsson never had the luxury of picking his spots, when he stepped out onto the ice, everyone on the other team knew to focus all their attention on him. Makar never had that problem, he has MacKinnon and Rantanen to divert the attention away from him. He's allowed to sit back and get lost in the play, which is exactly when he burns you. Nobody ever looked off Karlsson, and if you did, you coach was not going to be very pleased with you.
I'm not sure why Makar's defensive game is being talked about like he was way better than Karlsson. I actually found him to be far worse defensively this past playoffs than Karlsson was during the 2017 run. Makar was particularly bad against Tampa Bay in the finals, made a lot of egregious defensive errors in his own end, and at important times in the game as well. And for a guy who has the luxury of playing a much more conservative style than Karlsson ever did, that's simply unacceptable if the claim is going to be that he already surpassed him.