Your effective swing speed with the ornate is 2, not 1.5.
All of this information is in the chart, but this explanation might help you read it:
Ornate speed is 3.5. 150 Stam takes off 5 clicks (150 / 30) at .25 each (3.5 - 1.25 = 2.25). 30 SI takes off another tick at .25 bringing you to a total of 6 clicks off (3.5 - 1.5 = 2) for a swing speed of 2s at full stam. With a weapon speed of 2s you swing 30 times a minute, so damage per second is .5 X your average damage per hit. Average damage per hit with an Ornate, which has a damage range from 18-20, is 19. .5 X 19 = 9.5.
Radiant speed is 2.5. 150 Stam takes off 5 clicks (150 / 30) at .25 each (2.5 - 1.25 = 1.25). You can't reduce weapon speed below 1.25. With a weapon speed of 1.25s you swing 48 times a minute, so damage per second is .8 X your average damage per hit. (Incidentally, this is 160% of the speed you are swinging the ornate). Average damage per hit with a Radiant, which has a damage range from 12-14, is 13. .8 X 13 = 10.4.
At 180 effective stamina your ideal weapon for damage output per second is something with a weapon speed of 2.75, so for swords either daisho or hatchet, both of which have an 11.20 DPS at that level, more than either the radiant or ornate -- however for fighting multiple mobs I prefer a weapon with whirl wind.