I honestly don't think you can ever say "fireball spamming" isn't zoning. Even newer players, or "scrubs" who use them excessively are trying to zone with it, they just don't know how to use that to their advantage. People spam them because they think it helps them somehow, otherwise they wouldn't do it. In most cases when someone is spamming, if they aren't thinking in specific terms of zoning, they are trying to keep someone away and score free damage, which is a basic part of zoning. Fireballs are very important tools, that everyone tries to use, to different degrees of effectiveness of course. I think the major difference between a player who is good at zoning and someone who isn't, is if they recognize what they are using the fireballs for and try to make that work to their advantage.
In terms of melty spam, I think it still has its uses, making someone have to shield keeps them from doing something else, the thing that makes them weaker is they are easy to punish.