...Both are just X damage in Y seconds. And they're typically already quite high PPGCD.
Goring Blade, for instance, is 705 potency in total. Royal Authority, tied for the second strongest combo skill, is just 420 potency.
Even with the DoT devalued following level 84, a Goring Blade combo is therefore 401.7 ppgcd, while Royal Authority->Atonement is still just 363.3 ppgcd.
You'd have to lose over 5.3 seconds of the DoT for Goring Blade to not be worth it (though even then, because Royal Authority only reaches that ppgcd if it gets all 6 steps in, you'd only really drop Goring Blade from if you'd have lost more 13+ seconds out of Goring's 21... in which case you wouldn't have time to use but a single Atonement anyways, at which point it's just 335 ppgcd).
You don't need DoTs to be ridiculously OP to be useful or enjoyable. They just need to be just strong enough that their buyback period (the period after which they outperform the next best option) isn't too often eclipsed. They're already well designed for flexibility and openness to nuance (though it must still come from context) compared to other options by being, effectively (A) soft-CDs (B) with, in essence, a separate cooldown per target (up until replacement by one's AoE [combo]).
Ehhh... not quite.
If Storm's Eye still capped at only a single application's worth of duration, that'd be true, but now Storm's Eye can go up to 60 seconds between one application and the next (rather than 21 seconds), and it doesn't punish you for refreshing it more often than 1 in 4 combos so long as one has no more than 30 seconds of duration at the time. On the other hand, Goring Blade completely wastes any remaining duration at time of application, must be applied per 1 in 3 combos per target, and effectively has a separate "cooldown" per target involved up until the point that Prominence combo outpaces it.
Turning Goring Blade into a (modern) Storm's Eye (or "Surging Tempest") buff could actually change its gameplay a fair bit, especially outside of unabated-uptime single-target situations.