I dove further into looking at this, and here are the attacks that the respective heroes cannot learn:
Erdrick
- Frizzle/Kafrizz
- Zapple
- Woosh/Swoosh/Kaswoosh
- Oomph
- Bounce
- Flame Slash
- Kacrackle Slash
- Kamikazee
- Psyche Up
- Accelerattle
- Bang
- Kaboom
- Hatchet Man
- Whack
- Thwack
- Metal Slash
- Hocus Pocus
- Magic Burst
Solo
- Frizzle/Kafrizz
- Zapple
- Woosh/Swoosh/Kaswoosh
- Oomph
- Snooze
- Bounce
- Flame Slash
- Kacrackle Slash
- Kamikazee
- Sizzle
- Psyche Up
- Heal
- Accelerattle
- Bang
- Kaboom
- Hatchet Man
- Whack
- Thwack
- Metal Slash
- Magic Burst
Eight
- Frizz/Frizzle/Kafrizz
- Zapple
- Woosh/Swoosh/Kaswoosh
- Snooze
- Bounce
- Kacrackle Slash
- Kaclang
- Psyche Up
- Bang
- Kaboom
- Hatchet Man
- Whack
- Thwack
- Hocus Pocus
- Magic Burst
Luminary
- Woosh/Swoosh/Kaswoosh
- Bounce
- Kacrackle Slash
- Kamikazee
- Psyche Up
- Accelerattle
- Kaboom
- Hatchet Man
- Whack
- Thwack
- Hocus Pocus
- Magic Burst
It's a lot, isn't it?
With the attacks on all four lists, none of the Heroes learn them, they're learned by other party members and NPCs. So Hero is not just a composite character across the protagonists, but across the entire series.
When people are talking about a composite character, I think the insinuation is more that the character would draw from all or most of the characters within rather than eliminate the unique aspects of each. I mean I've seen several people suggest the character would have some version of the Min Min kick, for example.
That's why people are raising comparisons with the Earthbound and Castlevania characters, or the Links, or the Heroes. All those characters are amalgams that join material from multiple characters, not eliminate the defining facets of each. Obviously you can't include every aspect of every character, but whoever is saying the character would be sanded down to have no discernibly unique elements at all is voicing a different rhetoric.