or why only those with dragon blood even attempt to say dragon words

That’s not a requirement. Ulfric is right there. The Greybeards are right there.

Being Dragonborn just lets you eat dragon souls to gain literacy.

how shouting dragon words changes reality

For most of users it just emits violence from their mouths, which seems pretty redundant, since it’s something Nords didn’t ever have any problem with using their hands.

Let me guess… someone stole your sweetroll.