budru,
Most of what are describing are muscle mass areas. Horses won't gain muscle and have that overall roundness without work.
Also what is he, some of your lighter breeds-Arabs,Saddlebreds,Tb's never do get as rolly polly as your heavier types and ponies
Again-pot belly check for worms, and do know that worms can have a resistance to daily wormers or if you don't rotate the drug in the paste kind.
This link may help you determine his actual weight/condition.
How to Body Condition Score (BCS) Your Horse