I've been debating over how to frame this topic between the tank angle or just outright saying that I don't think keystones should have any damage ratio at all, but since the idea relates to tanks mostly anyway I think I'll go from this one.
Tanks have almost no variety between which primary tree they're allowed to take because of how the Resolve tree is set up. They have a little more wiggle room with their secondary options but Resolve primary is basically mandatory. You can take Grasp or Aftershock in your lane and maybe Guardian as a support. But the first two dont really give tanks the versatility of rune selection that could help them opt into better laning, because both of them require that you get into melee to use them meaningfully, while fighters have a rune that directly counters one of them.
For contrast, on my usual champions, I have at least 3 pages with keystones in different trees that I can opt into. Illaoi has one in *all five* trees that she can use well. Juggernauts probably have more versatility in Runes Resorted than any other class, and it does a lot to improve their viability that I don't think I'm vocal enough about appreciating. I can choose what I want on a per game basis and I am rewarded for using the system smartly.
A big part of this comes down to scaling. Keystones are a pretty big driver of damage creep not just because they add so much base damage, but also because they scale so well. This actually hurts the variety of choice more than it helps; because tanks are completely barred from non-Resolve choices due to not having the damage to make them valuable after ten minutes, while simultaneously losing too much in durability because they didn't run Resolve primary(which is another topic I'll cover later). You couldn't really justify, for instance, taking Comet on Ornn against a ranged champion so you have better odds of winning a poke war, because a big part of Comets value is in the scaling. The only time this wasn't true is when a poke spell on a tank is completely out of line and extra damage just adds insult to injury, like Sions E.
To me, keystones should be a lot more minor, with their power mostly being in an early game contribution and then your items taking the main focus. Removing their ratios would actually open them up a lot to a lot more champions, in my opinion, because there's less of an opportunity cost in what you're missing out on. And tanks, particularly solo lane tanks, would benefit massively from that sort of change.