I need to wall-of-text this. Sorry.
Consider Rune A (copyright 2024, Rune Naming Institute of Isola Sacra)
Rune A:
Project a magic circle on the ground. After a delay of 3 seconds, everyone in the circle takes damage.
That sounds pretty clunky and unwieldy, right? But that can be balanced, because it could deal slightly more damage to compensate for being unwieldy. Now there are suddenly situational uses for such a rune:
If you have a rune that roots enemies to the ground, then rune A is good. If you’re in a position where lots of enemies have to pass through a choke point, rune A is good.
Let’s say my gear has the following runes:
Rune A (as above)
Rune B:
Deal a small amount of damage. Debuff the target for a short time, causing it to take a percentage extra damage from everything that hits it in the next few seconds.
Rune C:
Deal a fair bit of damage. Deal extra damage if it hits a debuffed target.
Rune D:
A fast-casting rune that deals moderate damage, but also drains your stamina and poise.
Rune E:
An instant lightning bolt with no travel time that deals good damage, but has a long after-animation that can’t be cancelled (rumbling thunder, dark clouds seeping out of your sleeves, all that good stuff). You’d better be sure this kills the target, or it will leave you extremely vulnerable.
Individually, all of these would be, in most circumstances, inferior to a simple fireball. But if you chain them correctly, and if you have good situational awareness and make the right tactical decisions, together, they form a whole that is greater than the sum of its parts and is far more effective than just spamming fireball. For example, the fact that rune A deals damage on a delay means you can make better use of rune B’s window of opportunity.
Runes need mechanical distinctions, because then synergies can be discovered and actual builds can be crafted. I’m certainly not necessarily against cooldowns, but mechanical distinctions (such as, but not limited to, conditional effects) are more important.