Because that wasn't your original statement. You keep saying that using Succor is a potency lose of 290, regardless of what Succor would have replaced and in your initial argument, you say that you lost 290 potency from Succor and an additional 70 from the 1st tic of Biolysis, implying that Succor would have replaced a Broil and not a Biolysis, which is what makes the argument false because either Biolysis would have been used in place of Succor in the 2nd example, or you wouldn't need to use Biolysis and it would be the same potency loss as the 1st.
Now, you're trying to argue that DoTs aren't more forgiving than using a nuke because you wasted a GCD on a heal, which doesn't make sense because a heal is neither a DoT nor Nuke so its inclusion doesn't change anything. Using a GCD on a heal is a DPS loss, period. The only thing that matters is what that Heal is replacing, so either a DoT or Nuke. Missing a Nuke is more punishing because you lose out on its entirely potency, whereas missing a DoT only delays its total potency by 1 tic, hence its more forgiving because you are losing less potency than that of your nuke. The only way that your argument would be true is if the DoT was a GCD Nuke that dealt its full damage upfront and was delayed by the use of a GCD heal and even than, you'd be missing the 700p from that Nuke vs the 290 potency you keep falsely arguing about but since DoTs don't work that was, you only need to account for the 1 tic in delay vs the 1 nuke delay.
You can try and argue otherwise but the fact is you're just wrong. DoTs are more forgiving because you only lose 1 tic of damage when delayed by using the GCD heal or nothing vs a nuke losing its full potency.