He looks like a section B welsh to me. The very welshy looking ones are the section As. The section Bs are more show pony looking than the As which look very "Thelwell". Section Cs & Ds are totally cobby like Vanners.
Your mare is carrying alot of weight whereas the OPs pony is lean & young. You would be amazed at the difference it makes. To me, your photos only confirm my thoughts. My friends had a section B stud farm & I helped them pick out their foundation stock. Their first & junior stallion was very lean as he was a terrible fence pacer prior to their acquiring him.
Now I can see the OP's pony being grade, partbred or section B. There isn't a whole lot of difference in the ring between the quality grades, section Bs & the partbreds looks-wise though maybe in the US there is a big difference. I come from South Africa where there is a flourishing welsh population with many old imports from top foundation UK stock. I had an imported Anglo Arab as a child & many years later, I had an international judge comment to me while watching him compete that he looked like one of the true old welsh bloodlines (not knowing that I had owned him as a youngster). I smiled.
Well he is a handsome guy, that's for sure! I have a painted half welsh that I bred and raised myself and taught to drive. He is great. Welsh breeds are so cute - you just want to go up and kiss their cute little noses! He's the only pony in my herd but he things he's twice his size.