It is a mistake, because if you can't do "1.0 - z" or "0.5 * A", I don't know why you have operator overloading at all. What types with useful binary operators don't need to interact with scalars? Sets? Sequences? There aren't many math-y things that don't need numbers. The absence of complex values and matrices makes me sad, and I can list a dozen more on top of those.

Yes, static typing would be a huge change, but I think you're greatly exaggerating the complexity of multimethods for (only) binary operators. You don't want to do it, which is fine. It's your language, and you don't owe anyone anything, but be honest about your rationale.

You've already got a failure path to report errors when the types don't work, so falling back to a single global table of "first_type x second_type => function" is not more "huge" than anything else. You don't need scoping for operators like this, so it's literally one table. You can see the code in your head as you read this. I'm sure you could fill in the details or imagine some other simple implementation if you wanted to.