Valid point! I’d like to hear more regarding this concern. While I don’t necessarily view what I referred to as “interpreting the gaps” as synonymous with “legislate”, IANAL and would appreciate professional opinion here.

Well, for example, the SEC has used a law from 80 years ago about retaining memos as justification for billions in fines against companies whose employees used whatsapp to say "the market is crazy" (or similarly benign things). All they did was "fill in a gap" to make this totally new law.

IMO The rule of law derives from precedent. Prior to courts there was the rule of the monarch. The common law then developed as courts resolved disputes. It was all gap. The authorities would say the accused did something wrong and should be punished, and the courts came up with things like “murder” and “negligence.” Statutes are a relatively new way of making laws. They’re crude. Rather than simply resolving a real dispute based on the facts of an actual situation (and limiting the scope to the same or similar situations), legislators twiddle their thumbs and prospectively guess at what situations might occur and which words may address a multitude of unpredictable nuances. Statutes are pretty terrible because they’re so hard to refine. If a situation bumps against the plain language of a statute, the courts are essentially compelled to absurd and unjust results. However, that’s democracy. The people say they want the power to make the law, they say they want the clarity of a statute over a law book, and their errors are better than an overthrow of the system.

Precedents binding multiple courts is also relatively new (about 2.5 centuries). Before that, each court was effectively an island.