You can't really say that Lowell has had a huge season and then turn around and say Ortiz carried the lineup by himself. Ortiz has had a great year, and I do think that he's the MVP, but defense counts too. Lowell has 5.5 Win Shares on defense, while Ortiz has 0.1. Seems to me Lowell's overall game has put him on par with Ortiz's overall game this year, IMO.
The only thing Ortiz is down in this year is home runs. OBP, OPS, XBH, look to all be new career highs for Ortiz.
But I tend to agree, I just think Lowell gets more consideration because he plays defense and is having such a consistent offensive season.