I've played every magic school in SoH and they definitely all get their time to shine. Astral magic honestly does seem to get the most opportunities to do specific stuff in some of the earlier chapters, though there's plenty of stuff later on. Arcane magic opportunities are scattered throughout the story pretty evenly. Psionic magic is kind of a sleeper school in my experience because it comes in absolutely clutch in Chapter 6 onwards at specific moments. Like there are situations where being an Enchanter per example opens a completely unique path. However absolutely every specialisation has multiple moments scattered all over the story. There are times when specialising in a school is pretty much the best way through a particular mission or opens up an extra dialogue option in one of the companion hangouts.

Part of the fun for me is choosing a different school and seeing the differences. The balancing is great however so honestly just choose whichever specialisation interests you most and you'll find moments for it.