Question about attack speeds

So I finally maxed out my Heide.... and I don't see why she's so sought after. Her speed is terrible, and it feels that her DPS must be garbage compared to other 5*s. So my main question is this.... what is the actual speed of S, A, B, C, D, E ratings? I know that attack animation is also factored in, but there should be a general idea of what each rating does framerate-wise.... if anyone has taken the time to figure it out.

My max Meg feels like she does more damage than Heide, but idk.... I'm not asking for exact data, but the general perception of how the speed mechanic works.

i think you can test this by doing quests when you only deploy one unit.

they must be the same type though.

highest % at the end has most dmg

I've found that there are many more than 6 speeds in the game. There is a point system behind those letter values that cover a spread (If you'll notice Stray cat is faster than Angela & both have "S" ranked speed). I'm actually working on a ranking system that will help determine the success rate cards have against the different types of monsters (ground, air, sea). Because abilities like slow and knockback can eliminate a speed deficiency, or boost a card's effectiveness exponentially it's hard to tell what the actual numbers translate to in-game. I've found that Achillea already a B in speed who also has knockback and relatively strong attack is at the top of the list against ground monsters of all 4* and 5*. I've found her to be more effective in fact than Sofia even, a 5* that is coveted for her ground attack strength, but has only average speed and no abilities.