One of the things that adds significantly to prime "grade"
ribs & loins is a very thick heavy fat cap. Even top choice will usually have a pretty significant fat cap. For these high quality grades you usually pay for it with the fat cap on and then its trimmed off at your request/expense. I suspect you may have gotten a lower select grade roast. The fat cap will also vary from 1st cut through end cut.
For a special X-Mas dinner, I personally would splurge for a real nice well marbled top choice roast from a private butcher. When you think about how much work goes into the "entire" meal from start to finish a few extra bucks may well be worth it.