It's really not either one of those things. Each cliff is a +40 drop (cliffs in other stages are typically +30), so in Ryu's case you just add 40 damage to his Izunas as you would with any standard juggle or combo that sends them flying off. An izuna is 80 NH, 120 HiC, so 120 + 40 = 160. Nothing weird going on there.
Goarmagon: No. A HiC Izuna off of the Lost World cliffs nets 160 damage. So on default/Normal 300 life setting, it's still over half of a full health bar.
Puño de Leyenda: Those were my two favorite parts as well! Something about that hop made it all work so well.