I’ve never understood the chest/tri’s and back/bi’s routine, I gave it up almost 20 years ago (it didn’t last long). I’m not saying you’re wrong and a lot of people still follow that formula but I think it’s an old school mindset that hasn’t gone away.
I purposely do back and bi’s and chest and tri’s as far away as I can from each other. For example, I did chest and legs today, traps/bi’s tomorrow, just cardio on Sat due to work, tri’s/shoulders on Sun, and back/lats on Monday. Then repeat.
I want to be able to get the most out of each muscle group and obviously if you do tri’s/chest and back/bi’s together than one of them will suffer since they’re secondary to each other. When I did bi’s and back together I wouldn’t be able to lift as much or do as many sets in bi’s if I did back first or vice versa compared to separating them a few days between. Why not maximize each muscle group by giving them time to heal between days?
I definitely benefited from doing it that way in both strength and size.