Marius was told what even HP and Def-based skills arte depends on attack too. They never will tell to us how this work exactly because its a part of their monetization thing (and it may be changed anytime a little due game balaning without complains from coomunituy side).

Theoretically, all dmg in game mainly depends from atk vs def calculation. All other stats are just a modificators for this calculation. 

Type HP or Def-based champions just means what this guys are have more HP or Def in their stats then other champion types.

I noticed same thing with Executioner and Sir Nicholas too. S.Nick with 50% atk buff does a lot more dmg with his "purely" HP based skills, then without this buff.

That means that all this "Damage is based on [X]" is trash?