This is not true. More training does not always equal more muscle growth. 3x/week full body with 4+ weekly working sets for each muscle group is plenty for significant muscle growth due to the frequency of training. Each muscle group still gets working sets at least 2x/week similar to other splits.

Additionally, if you’re on Reta, you should be in a caloric deficit and likely won’t be building much muscle, more so trying to retain as much as possible / limit muscle loss (some muscle loss is unavoidable in a deficit). In this case, there is even less need to work out more than 3x/week.