Pretty nice that you ignored all the other examples I have where gathering storm is better. Here's a more focused point on my example from throwing more than 1 spell into the mix.

E has a 1:1 AP ratio at full charge. At 30 minutes, gathering storm gives 48 AP. That means if you do more than just 1 Q at your 30 minutes example, you're already doing at least 38 more damage with gathering storm. This also nets you 67 health you otherwise wouldn't have. Damage and health is increased further to 62 (52 more damage!) and 87 respectively if you have Deathcap. All this means that even if you're playing bursty one-shot vlad, gathering storm is better at your given time frame

At 20 minutes, gathering storm gives 38 extra damage on an E-Q combo. At that point, scorch will still do more damage as long as you're at least level 5. But once you hit 30 minutes (or do another spell rotation) gathering storm is going to be superior. Scorch has its use: early game. Gathering storm has its use: late game. Vlad is traditionally a late game focused character, and scales incredibly with AP, so you can't just cut-and-day say that Gathering Storm is "isn't worth it. Ever." even when it provides superior damage after 30 minutes, even in a burst combo. It's "mathematically" superior at that point, so you just plain can't say it's never worth it when it has a clear point where it is worth it.

They both have their uses. Like I said, if your goal is to snowball and end the game before 30 minutes, by all means use scorch. But don't just ignore gathering storm because scorch is better in your edge case of poking with a single spell at 30 minutes.