Ok, that appears to be a correct oil. So you should do those compression tests to help sort out the issue from rings vs valves. A borescope to look at the cylinder threw the spark plug holes. I just got a cheap $30 one on Amoron - there are way better ones for a little more money.
Compression appears low to me - rings not seated more likely than all the valve seats are weak/bad plus issues with valve stem seals allowing oil consumption. Check your valve lash while you are at it. I set mine on the loose side - better to hear them than to burn them. What pistons did they use - maybe some low compression ones for turbo/supercharged race tractors.
I'd be asking the people who did the work - that amount of oil consumption and low compression with 2500 miles on the clock isn't right. If they try and tell you its normal then I say they owe you a kiss after being screwed.