In terms of the way he looks, I can feel his ribs and if I pinch the fur around his ribs it feels nothing more than skin. He has a waist when looking from above
If that's how he looks he probably isn't overweight, because that sounds good in terms of body condition. If you do an internet search you'll find lots of charts showing body condition from underweight through to obese. I bet your boy will come into the ideal category.
Cockers vary a lot in build and height, from pocket rockets that are slim and fit at 9 or 10kg up to those who are several inches taller than breed standard height and weigh more than the breed standard average even when slim. Vets often seem to go by breed standard when determining if a dog is overweight, rather than using their eyes and some common sense