But why should FP be the basis for understanding?

Let's say I run a CS department. And let's say that I've accepted that what my department is really doing is jobs training for software engineers. Well, what are their jobs going to be, imperative or functional? For most of them, for most of their careers, the jobs are going to be imperative. Why should we start with FP?

You could say "FP is better", but then we're back at the OP's point. FP is better for some things, and worse for others.

For you to say that FP should be the starting point, you need to show that FP is better for the majority of programming situations, or else to show that FP is the better way to learn programming for the majority of students. I have never seen anyone seriously attempt to show either one. (Some argue "it fits how we think better", but what they mean is that it better fits how they personally think, ignoring that different people think differently.)

It’s about rope. Imperative languages generally give you a lot of flexibility (for x or y) and, therefore, rope to hang yourself. I don’t believe that starting students here, from a pedagogical perspective, is a good strategy. FP languages/paradigms, on the other hand, are all about restrictions(immutability, side effects, etc), and thus less rope. Less places to hang yourself, so to speak.

Also, even though, as you’ve stated sw engineers tend to work in an imperative environment (which I’m arguing is an artifact of their formative years), junior sw engineers should at least start with a bit of trepidation to use that rope (if only in their heads).

Plus, utilizing a functional style (and understanding the whys of functional style, where pragmatic) would improve many aspects of industry (e.g reducing the friction of adding tests - did I mention that I love tests??)

This rope only matters for production oriented systems. Most programmers are doing quotidian processing tasks. Manipulating CSVs, processing data to get statistics on, plotting points on maps, maybe writing a simple automation. Almost every software engineering class I read about when I was a graduate student teaching undergrad classes spent time discussing the pitfalls of the "rope of mutability" and explicitly discussed the idea of immutability to make this kind of programming safer. I agree with another poster that it's just much easier to teach general programming skills and thinking procedurally. I do think that programmers have to unlearn some of this when writing production-grade software, but most programmers will never write anything like that.