I found a meta analysis that studies this exact question. The conclusion: "When comparing studies that investigated training muscle groups between 1 to 3 days per week on a volume-equated basis, the current body of evidence indicates that frequencies of training twice a week promote superior hypertrophic outcomes to once a week. It can therefore be inferred that the major muscle groups should be trained at least twice a week to maximize muscle growth; whether training a muscle group three times per week is superior to a twice-per-week protocol remains to be determined."
The effect size on hypertrophy was 0.49 ± 0.08 vs. 0.30 ± 0.07. Training each muscle group twice per week yielded 63% more gains than training each once per week, even after controlling for total weekly volume.
In other words, bro-splits (defined as training each muscle group once a week on specific days) are horrible. Every muscle group needs to be trained twice per week minimum. Since your body doesn't know that weeks exist I would say a 72 hour maximum latency between workouts, to be precise.
Also, anecdotally, training at higher frequencies with lower volumes dramatically reduces the incidence of DOMS.
Here's another meta analysis that supports training each muscle group 3x/week for untrained individuals and 2x/week for trained individuals: http://europepmc.org/abstract/med/12618576
Here's a third meta analysis that says strength development in collegiate/professional athletes is maximized by training twice per week, at ~85% 1RM for a total of 8 sets per week per muscle group.
Don't know if any of these studies looked at doing 1 set per day 7 days per week though. Or looked at just exercising every second day instead of arbitrarily having an extra rest day every seven due to the prime number of days in a week.
Here's a study that shows muscle protein synthesis spikes after training but returns almost to baseline after 72 hours. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC1474228/
Another study that shows running concurrently with strength training reduced the benefits of strength training by a third, but cycling concurrently did not. https://journals.lww.com/nsca-jscr/Fulltext/2012/08000/Concurrent_Training___A_Meta_Analysis_Examining.35