Spell intensity

I'm a vanilla campaign enjoyer that posts here on occasion to ask the masters about certain topics and occasionally share my knowledge and opinions with the newest of players, this post is the former. Thank you all for your answers in advance.

The other day I had someone reply to one of my comments with a damning claim that spell intensity does not apply to spells that inflict direct damage. He claimed extensive testing but offered no evidence other than the claim that because direct damage spells show both the original and boosted numbers that they aren't actually affected by the increased damage.

I didn't try to refute it, because I'm still a complete noob at \~3k hours across wh2/3 and have also done no testing myself despite not witnessing his testing either. I just feel like I've spent enough time lurking this sub that I would have picked up that knowledge at least a year or two ago.

Tl;dr can anyone provide evidence on the effect of spell intensity on direct damage spells?