In terms of scale and advanced terrain weight, I though Taos (pre-Kachina) and Alyeska were the closest analogies. A-Basin is another one now. I would have said A-Basin is smaller, but that was before the Beavers expansion which I have not skied yet.
But I agree that people go to Portillo with the mindset that it's larger than it really is. Qualitatively it's still better than the 3 areas out of Santiago IMHO.
It's a really beautiful spot - no question. And full of history. Perhaps the least crowded major resort that I have skied with almost zero-day skiers and just a few overnight guests.
But it would be hard to spend a week there in marginal conditions. FYI - I was not able to ski the left-hand side off of the traverse.
However, all of the slingshot lifts were open. Condor and Las Vizcachas did not serve overly difficult terrain but provided better drop ins to the Lake Chutes, and some low-angle untracked. Roca Jack and El Caracara were much steeper but were mostly confined to the areas immediately surrounding the lifts.
I thought this article in Freeskier
was as good of a guide as any.
I think Taos has a larger footprint and a lot more interesting terrain off of its ridges. Plus its steep bump runs. I hiked Kachina once back in 2010 during perhaps their last great snow year - pretty worthwhile.