I agree with you when you say that Heian shouldn't be considered as kata for beginners. These serie contains lot of Kanku/Kushanku movements, Bassai/Passai...
But I agree that they are basic: because what supports a house is the base. Without it the house will not "stand up".
Understand what I mean? I think so
What for knowing advanced katas if you don't know the bases that compose it. What do we learn first in karate? Isn't it kihon, and it means: Basic!!!!
With strong roots you will grow up strong too!