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Notice rules are ordered. You don't optimize until you know you need it. They started with a data structure they though would be fine. Clearly it was fine since it worked and they decided it was later worth optimizing.

Rule 5 is superseded by Rules 1 & 2. Without the measurements to back it up, you're chasing phantoms.

Rules 1&2 are about speed, not memory. But also, what do you think the issue with measurement is in this case??

The existence of 1.1.1.1 speaks to a much larger design problem. If you want to talk about what should have been done, you need to step much, much further back.

I don't want to step back and go off topic

"Should" cannot be evaluated in a vacuum. The only thing that would be off-topic is pretending that it can be.