Had a talk with Chaichen the Legend formerly known as Chaichen the Legend before HOTL3 was relaunched by Thor and he told me HR/DR and MAGIC/COST is not really that crucial as the damage is more or less taken care of by Class Level instead.
I don't disagree with one of these wise sages in the game, especially when I found fighting gradually easier for me as I gen up. It could be due to the higher "E" in the skills or the increase in Class Level itself. There is no way I can test it so I can't see how much it impacts us in damage dealing.
What I can do is, though, test out if there is any differences in damage dealing at 3 different MAGIC/COST levels. I did my damage test on good ol' Almuhara, who was standing there doing nothing useful today.
My results are as follow;
With Magic: 56 Cost 64
With Magic: 168 Cost 15
With Magic: 270 Cost 9
I did several tests for each level but it will be too tedious for me to post every screenshot but I believe I have done enough tests to get a general feeling of the impact of these stats. My conclusion is that the Magic stat does affect damage, as it is obviously shown here in the screenshots but it appears to me that it is not on a straight-line, proportionate setting but rather on a curve that gives diminishing return on the high side. That means damage should be significantly improved from low to medium Magic but more gradual from medium to high.
Another conclusion you may want to draw from this is that, Rains of Fire sucks even at E7. As you can see, I hardly dent Almuhara even on a respectable Magic level of 270. Not only that following fireballs are not guaranteed (in fact, I get 2 balls 75% of the time), most crucially, they will be of half the damage of each of their precedents. Thus even if I have 4-5 balls guaranteed on each attack, I will be dealing next to nothing in damage from the 3rd ball onward, unless you consider dark green damage as something to cheer about.
Not surprisingly, Eken took my advice to ditch Fire and told me he is loving his new class.