Let me chime in on the leg and back training suggestion.
I was really fat with no definition, then got way too skinny with no definition. Then bulked up then lost it all training for a triathlon.
Afterr I started training legs and back 3 times a week, my
upper body started improving faster too.
In fact, even though I'm small, weak, little, and get scared easy right now, my upper body is looking the best it ever has. I attribute part of this to 3x weekly leg and back training. And this is in spite of the damage done and 20lbs lost from crappy training and barely remembering to eat for the last 3 months.
Seriously, don't train the abs if you don't want. But get those squats and deads - or the machine equivalents if you can't squat and deadlift.
I've said it before and will say it again. Squat, Dead, Bench, Row is all you REALLY need. If I was limited and could only do 4 lifts 3 times a week, those would be the ones I chose.