The "negative" or eccentric component's contribution to hypertrophy has been well known since the 80's. I took a look at the linked journal and zeroed in on the cohort.

"A total of 53 (25 male and 28 female) healthy university students ... who ... had not performed a structured resistance training in the past 6 months, participated in the present study." Ok; so, totally untrained/detrained individuals. This lends less credence to the usefulness of this study.

This study doesn't contribute to the advancement of exercise science and ignores neuromuscular adaptations, the stretch-shortening cycle, and/or lactate threshold effects of non-eccentric muscle contractions.

Depending on your sport or personal goals, a mix of different time-under-tension parameters and rest periods will get people closer to their desired health goals. The eccentric phase is just one part of the equation.

Saying this is "all you need to do" is wrong. The curious should examine the syllabus of the NSCA CSCS program.