I understand your point, Bostonian, and under the circumstances which you describe
I totally agree that what was offered to your child was better than nothing.
That said, working independently for a math competition gives the child a sense of belonging and identity: While the peer group does not exist in the child's classroom, it exists as a broader distribution and is comprised of contest entrants.
Allowing work on math at a competitive level may also be distinct from requiring a child to be routinely self-taught in mathematical concepts.
Therefore independent work for a math competition may be quite different than the socially isolating and autodidactic demands of a packet... even though the socially isolating, autodidactic packet may be euphemistically termed "independent work".
In general, gifted kids and advanced learners need and may benefit from "differentiated
instruction", not "differentiated
task demands", which may be seen as
punitive.
As tedious as it may be, I encourage parents to look beyond
buzzwords and learn the
5Ws of any gifted program or offering, in order to understand what their child will experience (and proactively assess it's potential positive or detrimental effects). This might help ensure that your child is receiving the opportunities needed to develop the 10 skills mentioned in the article.