You can learn to space with any character. Not sure why you think Link and Samus are the "best" for this. Sup boomfan.
Also, I think reading others is the most important yet most difficult skill to individually improve upon. Real talk.
Of course you can learn to space with any character. That doesn't mean that the learning curve is going to be the same for all fundamentals with each character. For example, Fox is probably one of the best characters to use to improve tent combo strategies. Nair off the tent -> upsmash is a technique that can be applied to many characters, but is most easily learned with Fox. I think that's because of his speed, which allows that combo to connect at a wide range of %s.
The reason I think Link and Samus are particularly good for spacing is because:
Link requires a safe distance from his opponent, or else he'll find himself dead very quickly, even against noobs. That doesn't necessarily mean a player has to rely on boomerangs and bombs, they can be fairly successful without them, but it just means that they need to choose their spots very carefully.
Samus has a pretty poor approach with very few disjointed hitboxes, and requires very precise timing and spacing in order to minimize the amount of "traded hits," which are particularly detrimental to Samus because of her lack of combo ability.
Other characters, particularly Kirby and Pikachu, can make many spacing mistakes, but can make up for it with their other natural advantages.
