In NES, the battles were horribly slow, and casting a spell on everyone (either all enemies or all allies) pretty much took forever since the spells were hitting one target at a time, and the game was displaying an effect information box between every hit. Leveling up HP and MP were very slow, and most of all, weapons and magic took ages to level up.

In FFII WSC and FFII Origins, the battle speed and group casting effects were greatly improved, and it was a lot faster to level up weapons. However, HP, MP and spells were still very slow to level up in those versions, greatly discouraging the use of magic.

In FFII DoS, HP pretty much increases on its own, so you don't need to worry about that, and the spells level up a lot faster. You still need to level up your party a lot, but it's clearly more tolerable in FFII DoS. Leveling up MP is still a bit of a problem there, but I usually solve that by raising the spell Sap on a high level and using it to drain the MP of my party members.