what I meant, the macro system should support hygiene, not necessarily that all macros in it must be hygienic. The syntax bits being manipulated come with an extra scope context, which means you get better preserved information about initial structure of your program; the more information macro has, the more it can achieve. And crucially, in a macro system capable of hygiene, you're not implicitly losing unhygienic capabilities. Implementing unhygienic macros in a hygienic system just means deleting all the scope information. Implementing hygienic macros in unhygienic system is a question mark. As (a somewhat imprecise) analogy, consider dynamic vs lexical scoping. If you have just lexical scoping support, you can mimic dynamic scoping with globals (since global scope is what's left when you delete other scopes). If you have just dynamic scoping support, implementing lexical scope is a question mark.

What Let Over Lambda calls limited power, is probably in reference narrowly to `syntax-rules`. It's not just that it's hygienic, but that it purposefully has no way to opt out of it (unhygienic capabilities in a hygienic system are trivial to provide; but they still need to be provided by language implementation) but what's even more limiting is that it doesn't let you write procedural macros, it's all arcane pattern matching and templates. `syntax-case` (part of r6rs) doesn't have these issues.