For Lady Gaga, it would be. If Born This Way, a 5-6 million seller is considered an underperformance for her, what would 3.5 million be?
An underperformance just means it did worse than expected which BTW did. However anything over the 3 million barrier for anyone who has a global presence is a win and I'd say if your local a 2-3 million would still be considered succesful for the artist. Now we know she probably aims for more but I don't think Gaga will be crying if only 3.5 million people buy the album