Unlike in most modern Christmas stories, where children being unable to see Santa raises more questions than it answers, here not being able to see Santa is part of the point—Santa has to remain a vague ideal, because the important thing is not the man himself but the happiness and optimism he inspires in children. Grandsanta, Malcolm, and Steve all have the same flaw of having made Christmas about themselves rather than the children, and it'd be so much easier to fall into that trap if they were able to receive any of the credit.
Arthur: This picture isn't of dad, or of [Grandsanta], it's of Santa! And as long as she gets a present, then he's real! And he came! —Wack'd
The way the four "Santas" are portrayed each represents a specific aspect of our ideal image of Santa and Christmas in general. It's shown that having just one aspect can lose focus on what makes Christmas special but together can create true Christmas magic.
Malcolm, the current Santa, represents the body of Santa, not only one of the first images that one would think of when they think of Santa Claus, but the hard working Santa as well. Always working hard and for a long time as well. But in doing so, it becomes more like a job and he's been doing it for so long, not only has he long forgotten the reason he's Santa, but in staying this long as Santa, he can't pass the job on so easily. A conversation he has with Steve is when he was young, Steve wanted a pool table, but Steve didn't write to him so he didn't know, hinting that he may have accidentally saw Steve as just another child rather than his own son.
Steve, the successor Santa, represents the futuristic Santa, a technologically advanced tinkerer who knows he has to advance the line of work Santa has to do in order to get the work done, faster, stronger and effectively. And for the most part, it works since it seems very plausible that this is the kind of thing Santa would do to get his presents out to everyone in time. But that drawback comes with being more in touch with computers and his workers than with actual people. He has trouble with children, something that's very important as Santa since Santa is supposed to bring hope to the children of the world as was when he had a difficult time talking to a spanish speaking child. It also goes with his character arc where he wants to be acknowledged by his father and that his contributions do work.
Grandsanta, the previous Santa, is the traditional Santa. He shows that the old ways with just a sled and a group of reindeer were the most efficient way since it was a tried and true method in the past coming with old style cloaking and magic to help the reindeer. The obvious flaw with this is that while the old ways are effective, times have changed, but he hasn't showing that he's tuned out from the world around him. He has an old map of the world, which isn't valid anymore since they managed to get lost several times, he doesn't give enough altitude on the sled so they can avoid skyscrapers so they wouldn't get caught, and most problematic of them which got him retired in the first place, he made a mistake during the Cuban Missile Crisis and almost caused World War Three. His motivation for even getting the present to the child isn't to the service of the child, but rather to show his family that it can be done.
And then we have Arthur, the non-Santa of the family who eventually becomes Santa by the movie's end, who is the caring Santa. While the least hands-on compared to his family, he still knows about the heart of Christmas seeing all of the letters to Santa and personalizing all of them the best he can. He's the one that kick starts the plot of the movie to get one single present to a girl because in his eyes, if one child doesn't get their present, then Christmas was a failure no matter what. But that does not make him immune to mistakes as well. The movie clearly shows how clumsy he is leading him into trouble and how he often needs the help of others. Thus his character arc becomes firmly established through his realizations, it doesn't matter who gives the present and how they get it to them, as long as "Santa" gets it to them and alongside his family, succeeds. Being The Heart of the family, he brings everyone together to save Christmas as it still requires compromise and support to make a Christmas miracle.
One Elf is registered as "82% Nice" when scanning himself to give a "56% Naughty" a half-decent present. Since he's probably breaking protocol doing so, it's not surprising he wasn't listed higher in the scale.
The film makes a big deal about Santa needing to keep his existence a secret because the adults don't believe in him and would think he was some sort of threat. With that in mind, how is it that the parents of all these kids seem completely unperturbed by the overnight arrival of all these gifts that they didn't buy?