Makar and Dahlin benefit lot from their teams PP, when looking points. But they also are big parts of those PP's. Makar of course benefits from MacKinnon, Rantanen and Landeskog, but he is also able to help those players way many others aren't. But same time Heiskanen also doesn't have similar PP to play with. I guess, he wouldn't be as good as those two are in PP, but he isn't the biggest issue in that PP. Also his points get disadvantage from Dallas' system, which is more defensive than others. It's not easy to make one on one comparison on points. They are all good to attacking side of game. Little different tho. And little with little different game systems. If you want to see Heiskanen's offensive game with similar freedoms to Makar and Dahlin, better look game, where they are behind in third period. He plays differently.
In defense difference is now bigger. And big part there is how they are trusted there. Heiskanen is probably best defensive defenseman in Dallas on even strength. And he is used like that. It felt like Oilers tried to avoid McDavid and Draisaitl to play against him. (Hard to prove, when all played so much.) He isn't strong as some guys close to goal, but he can defend fast players in very top level. There aren't many, if any, better in league.
I'm really waiting to see, what kind of futures these all have. I have always liked good two-players. Defenders and forwards. This generation of defenders is special. These all have potential to win Norris very many times.