Speaking strictly in terms of how valuable of an asset they are, Bedard is basically already in that group with MacKinnon/Matthews/Makar.
He's already practically a ppg player at age 18 on an awful roster. Right now, as an 18 year old Bedard probably puts up 90-100 pts with good line mates, he's already good enough to do that. I think when you consider how good he is already and his age, he might already honestly be the #2 most valuable asset in the league. As great as MacKinnon is, he is 10 years older than Bedard, Matthews is 8 and Makar is 7 years older. None are "old" but the reality is that careers are finite and guys often fall of in their 30s. Even in today's game where some continue to be stars into their late 30s its still a very real possibility. I feel that inherently you are more likely to get injured as you age and put miles on your body.
Given those realities I think if given a chance to start a hypothetical new franchise you might take Bedard over anyone not named McDavid. Obviously there would be some debate but I don't think anyone would call a GM crazy for taking the 18 year old kid with thaaat much potential who has already showed enough as a rookie that he is legit 100%
I think the asset valuations for players that are 25 on long term deals vs 18 get difficult, because it can require a lot of assumptions about your ability to retain the 18 year old well beyond his RFA years at a manageable cap hit.
But in the case of Makar vs Bedard as assets, Makar only has 3 years left after this season. So I think Bedard probably has the edge as an asset just because you're pretty much guaranteed to have him for at least 6 more years (and probably 8). And for 2 of those years, you're getting him at a significant discount (though Makar at 9M is a crazy good price too).
I would also argue that a player like Makar, who has enjoyed so much team success with a franchise, is probably more likely to be a career Avalanche than Bedard is to he a career Blackhawk.
Regardless of all of the above, I don't think you can reasonably look beyond the next 7-8 years or so when comparing players at these career stages. But we can try. Assuming they both resign with their teams until 2032-33 with the below assumptions, I think it's probably a coin toss until about 2030, then it's tips in favor of Bedard:
Bedard
2x4.5M ages 19-20
8x14M ages 21-28
Makar
3x9M ages 26-28
7x12.5M ages 29-35