You are ignoring the efficacy. The studies show that "Breakthrough" cases of vaccinated people who test positive for Delta can spread as easily as unvaccinated. Breakthrough cases represent the percentage of people who catch it. The other percentage are the people who don't catch it because of the vaccine. Thats what the efficacy rate is.
Here read this... it references the study you linked to...
And while vaccines are still extremely effective at preventing hospitalization and death from COVID-19, studies are showing that vaccinated people who contract the coronavirus, so-called “breakthrough infections,” may have viral loads as high as those among unvaccinated individuals, meaning they
can transmit the infection.
This differs from our previous understanding of COVID-19 vaccine effectiveness.
“When COVID-19 vaccines first became available, they demonstrated a great ability to prevent the recipient from contracting any form of COVID-19, which largely removed vaccinated asymptomatic and presymptomatic exposures from the equation,” Ammon told Healthline.
“However, the Delta variant has developed an ability in some instances to partially evade the immunity provided by vaccination, meaning there are more breakthrough infections in vaccinated individuals from the Delta variant than were seen from previous versions of the virus,” he said.
But it’s not all bad news.
Recent studies show the critical importance of getting the COVID-19 vaccine both for personal health and limited transmission.
The incubation period for the coronavirus is between 2 and 14 days. On average, COVID-19 symptoms appear around 5 days after exposure, but this can vary.
www.healthline.com